`nim c -r -d:useSysAssert -d:useGcAssert tests/testall` fails on OSX
I've disabled chronos on OSX from important_packages in https://github.com/nim-lang/Nim/pull/13954 because CI for chronos fails on OSX:

https://dev.azure.com/nim-lang/255dfe86-e590-40bb-a8a2-3c0295ebdeb1/_apis/build/builds/4234/logs/76

```

2020-04-11T13:10:46.5530120Z [1m[31mFAIL: [36mhttps://github.com/status-im/nim-chronos C[0m
2020-04-11T13:10:46.5530940Z [1m[36mTest "https://github.com/status-im/nim-chronos" in category "nimble-packages"[0m
2020-04-11T13:10:46.5531670Z [1m[31mFailure: reBuildFailed[0m
2020-04-11T13:10:46.5531940Z package test failed
2020-04-11T13:10:46.5532150Z $ nimble test
2020-04-11T13:10:46.5532510Z   Executing task test in /Users/runner/runners/2.165.2/work/1/s/pkgstemp/chronos/chronos.nimble
2020-04-11T13:10:46.5532960Z 
2020-04-11T13:10:46.5533560Z nim c -r -d:useSysAssert -d:useGcAssert tests/testall

...

2020-04-11T13:10:46.5643960Z CC: testserver.nim
2020-04-11T13:10:46.5644170Z CC: testbugs.nim
2020-04-11T13:10:46.5644370Z CC: testnet.nim
2020-04-11T13:10:46.5652800Z CC: ../../../../../../../../.nimble/pkgs/bearssl-0.1.5/bearssl/decls.nim
2020-04-11T13:10:46.5654090Z CC: ../../../../../../../../.nimble/pkgs/bearssl-0.1.5/bearssl/errors.nim
2020-04-11T13:10:46.5654510Z CC: ../chronos/streams/tlsstream.nim
2020-04-11T13:10:46.5654770Z CC: testasyncstream.nim
2020-04-11T13:10:46.5655000Z CC: testall.nim
2020-04-11T13:10:46.5655190Z Hint:  [Link]
2020-04-11T13:10:46.5655750Z Hint: 165288 LOC; 12.580 sec; 337.258MiB peakmem; Debug build; proj: tests/testall; out: /Users/runner/runners/2.165.2/work/1/s/pkgstemp/chronos/tests/testall [SuccessX]
2020-04-11T13:10:46.5657140Z Hint: /Users/runner/runners/2.165.2/work/1/s/pkgstemp/chronos/tests/testall  [Exec]
2020-04-11T13:10:46.5657490Z 
2020-04-11T13:10:46.5657700Z [Suite] Macro transformations test suite
2020-04-11T13:10:46.5657900Z 
2020-04-11T13:10:46.5658140Z [Suite] Asynchronous sync primitives test suite
2020-04-11T13:10:46.5658350Z 
2020-04-11T13:10:46.5658550Z [Suite] callSoon() tests suite
2020-04-11T13:10:46.5658730Z 
2020-04-11T13:10:46.5658940Z [Suite] Asynchronous timers test suite
2020-04-11T13:10:46.5659130Z 
2020-04-11T13:10:46.5659340Z [Suite] Future[T] behavior test suite
2020-04-11T13:10:46.5659530Z 
2020-04-11T13:10:46.5659740Z [Suite] Signal handling test suite
2020-04-11T13:10:46.5659920Z 
2020-04-11T13:10:46.5660130Z [Suite] TransportAddress test suite
2020-04-11T13:10:46.5660310Z 
2020-04-11T13:10:46.5660520Z [Suite] Datagram Transport test suite
2020-04-11T13:10:46.5660910Z /Users/runner/runners/2.165.2/work/1/s/lib/pure/unittest.nim(647) testdatagram
2020-04-11T13:10:46.5661400Z /Users/runner/runners/2.165.2/work/1/s/pkgstemp/chronos/chronos/asyncloop.nim(946) waitFor
2020-04-11T13:10:46.5661930Z /Users/runner/runners/2.165.2/work/1/s/pkgstemp/chronos/chronos/asyncloop.nim(278) poll
2020-04-11T13:10:46.5662450Z /Users/runner/runners/2.165.2/work/1/s/pkgstemp/chronos/chronos/asyncmacro2.nim(273) testBroadcast
2020-04-11T13:10:46.5663040Z /Users/runner/runners/2.165.2/work/1/s/pkgstemp/chronos/chronos/asyncfutures2.nim(407) internalCheckComplete
2020-04-11T13:10:46.5663440Z [[reraised from:
2020-04-11T13:10:46.5663770Z /Users/runner/runners/2.165.2/work/1/s/lib/pure/unittest.nim(647) testdatagram
2020-04-11T13:10:46.5664270Z /Users/runner/runners/2.165.2/work/1/s/pkgstemp/chronos/chronos/asyncloop.nim(948) waitFor
2020-04-11T13:10:46.5665140Z /Users/runner/runners/2.165.2/work/1/s/pkgstemp/chronos/chronos/asyncfutures2.nim(423) read
2020-04-11T13:10:46.5665740Z /Users/runner/runners/2.165.2/work/1/s/pkgstemp/chronos/chronos/asyncfutures2.nim(407) internalCheckComplete
2020-04-11T13:10:46.5666110Z ]]
2020-04-11T13:10:46.5666230Z 
2020-04-11T13:10:46.5666470Z     Unhandled exception: Timeout exceeded!
2020-04-11T13:10:46.5666740Z Async traceback:
2020-04-11T13:10:46.5667130Z   /Users/runner/runners/2.165.2/work/1/s/lib/pure/unittest.nim(647)                      testdatagram
2020-04-11T13:10:46.5667680Z   /Users/runner/runners/2.165.2/work/1/s/pkgstemp/chronos/chronos/asyncloop.nim(946)     waitFor
2020-04-11T13:10:46.5668230Z   /Users/runner/runners/2.165.2/work/1/s/pkgstemp/chronos/chronos/asyncloop.nim(278)     poll
2020-04-11T13:10:46.5668780Z   /Users/runner/runners/2.165.2/work/1/s/pkgstemp/chronos/chronos/asyncmacro2.nim(273)   testBroadcast
2020-04-11T13:10:46.5669370Z   /Users/runner/runners/2.165.2/work/1/s/pkgstemp/chronos/chronos/asyncfutures2.nim(407) internalCheckComplete
2020-04-11T13:10:46.5669830Z Exception message: Timeout exceeded!
2020-04-11T13:10:46.5670130Z Exception type: [AsyncTimeoutError]
2020-04-11T13:10:46.5670400Z   [FAILED] Broadcast test
2020-04-11T13:10:46.5670940Z     /Users/runner/runners/2.165.2/work/1/s/pkgstemp/chronos/tests/testdatagram.nim(560, 54): Check failed: getTracker("datagram.transport").isLeaked() == false
2020-04-11T13:10:46.5671780Z     getTracker("datagram.transport").isLeaked() was true
2020-04-11T13:10:46.5672080Z     false was false
2020-04-11T13:10:46.5672330Z   [FAILED] Transports leak test
2020-04-11T13:10:46.5672510Z 
2020-04-11T13:10:46.5672710Z [Suite] Stream Transport test suite
2020-04-11T13:10:46.5672900Z 
2020-04-11T13:10:46.5673490Z [Suite] Server's test suite
2020-04-11T13:10:46.5673680Z 
2020-04-11T13:10:46.5673910Z [Suite] Asynchronous issues test suite
2020-04-11T13:10:46.5674100Z 
2020-04-11T13:10:46.5674310Z [Suite] Network utilities test suite
2020-04-11T13:10:46.5674630Z 1.  lo0: flags = 32841 mtu 16384 state StatusUp
2020-04-11T13:10:46.5674920Z     IfSoftwareLoopback 
2020-04-11T13:10:46.5675400Z     inet 127.0.0.1/8 netmask 255.0.0.0 brd 127.255.255.255
2020-04-11T13:10:46.5675860Z     inet6 ::1/128 netmask ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff brd ::1
2020-04-11T13:10:46.5676390Z     inet6 fe80::1/64 netmask ffff:ffff:ffff:ffff:: brd fe80::ffff:ffff:ffff:ffff
2020-04-11T13:10:46.5676850Z 2.  gif0: flags = 32784 mtu 1280 state StatusDown
2020-04-11T13:10:46.5677130Z     IfIeee80212 
2020-04-11T13:10:46.5677400Z 3.  stf0: flags = 0 mtu 1280 state StatusDown
2020-04-11T13:10:46.5677680Z     IfHippiInterface 
2020-04-11T13:10:46.5677960Z 4.  en0: flags = 34915 mtu 1500 state StatusUp
2020-04-11T13:10:46.5678290Z     IfEthernetCsmacd 00:50:56:88:2C:AC
2020-04-11T13:10:46.5678650Z     inet 10.79.9.3/20 netmask 255.255.240.0 brd 10.79.15.255
2020-04-11T13:10:46.5679020Z 5.  utun0: flags = 32849 mtu 1380 state StatusUp
2020-04-11T13:10:46.5679300Z     IfOther 
2020-04-11T13:10:46.5679700Z     inet6 fe80::818d:25b8:fc83:cb94/64 netmask ffff:ffff:ffff:ffff:: brd fe80::ffff:ffff:ffff:ffff
2020-04-11T13:10:46.5680200Z 6.  utun1: flags = 32849 mtu 2000 state StatusUp
2020-04-11T13:10:46.5680470Z     IfOther 
2020-04-11T13:10:46.5680880Z     inet6 fe80::d23f:d69b:8452:8c2d/64 netmask ffff:ffff:ffff:ffff:: brd fe80::ffff:ffff:ffff:ffff
2020-04-11T13:10:46.5681350Z 8.8.8.8 via gateway 10.79.0.1 src 10.79.9.3
2020-04-11T13:10:46.5681560Z 
2020-04-11T13:10:46.5681760Z [Suite] AsyncStream test suite
2020-04-11T13:10:46.5681940Z 
2020-04-11T13:10:46.5682140Z [Suite] ChunkedStream test suite
2020-04-11T13:10:46.5682320Z 
2020-04-11T13:10:46.5682510Z [Suite] TLSStream test suite
2020-04-11T13:10:46.5683430Z Error: execution of an external program failed: '/Users/runner/runners/2.165.2/work/1/s/pkgstemp/chronos/tests/testall '
2020-04-11T13:10:46.5683930Z stack trace: (most recent call last)
2020-04-11T13:10:46.5684370Z /private/var/folders/24/8k48jl6d249_n_qfxwsl6xvm0000gn/T/nimblecache/nimscriptapi.nim(165, 16)
2020-04-11T13:10:46.5684900Z /Users/runner/runners/2.165.2/work/1/s/pkgstemp/chronos/chronos_7298.nims(25, 8) testTask
2020-04-11T13:10:46.5685400Z /Users/runner/runners/2.165.2/work/1/s/lib/system/nimscript.nim(260, 7) exec
2020-04-11T13:10:46.5686520Z /Users/runner/runners/2.165.2/work/1/s/lib/system/nimscript.nim(260, 7) Error: unhandled exception: FAILED: nim c -r -d:useSysAssert -d:useGcAssert tests/testall [OSError]
2020-04-11T13:10:46.5687580Z        Tip: 1 messages have been suppressed, use --verbose to show them.
2020-04-11T13:10:46.5688020Z      Error: Exception raised during nimble script execution
2020-04-11T13:10:46.5688280Z 
2020-04-11T13:15:18.6274920Z [32mPASS: [36mhttps://github.com/c-blake/cligen.git C                     [34m ( 2.04 sec)[0m
2020-04-11T13:15:18.6276190Z [32mPASS: [36mhttps://github.com/samuelroy/coco C                         [34m (24.98 sec)[0m
2020-04-11T13:15:18.6277160Z [32mPASS: [36mhttps://github.com/PMunch/combparser C                      [34m ( 3.00 sec)[0m
2020-04-11T13:15:18.6278090Z [32mPASS: [36mhttps://github.com/LemonBoy/compactdict C                   [34m ( 3.55 sec)[0m
2020-04-11T13:15:18.6279050Z [32mPASS: [36mhttps://github.com/alehander42/comprehension C              [34m ( 2.99 sec)[0m
2020-04-11T13:15:18.6280490Z [32mPASS: [36mhttps://github.com/LemonBoy/criterion.nim C                 [34m (35.07 sec)[0m
2020-04-11T13:15:18.6281420Z [32mPASS: [36mhttps://github.com/FedericoCeratto/nim-dashing C            [34m ( 1.86 sec)[0m
2020-04-11T13:15:18.6282350Z [32mPASS: [36mhttps://github.com/docopt/docopt.nim C                      [34m (19.11 sec)[0m
2020-04-11T13:15:18.6283330Z [32mPASS: [36mhttps://github.com/jackmott/easygl C                        [34m (16.20 sec)[0m
2020-04-11T13:15:18.6284310Z [32mPASS: [36mhttps://github.com/mattaylor/elvis C                        [34m ( 3.79 sec)[0m
2020-04-11T13:15:18.6285220Z [32mPASS: [36mhttps://github.com/fragcolor-xyz/fragments C                [34m ( 1.95 sec)[0m
2020-04-11T13:15:18.6286270Z [32mPASS: [36mhttps://github.com/alehander42/gara C                       [34m ( 3.46 sec)[0m
2020-04-11T13:15:18.6287540Z [32mPASS: [36mhttps://github.com/Vindaar/ggplotnim C                      [34m (52.02 sec)[0m
2020-04-11T13:15:18.6288480Z [32mPASS: [36mhttps://github.com/citycide/glob C                          [34m ( 7.31 sec)[0m
2020-04-11T13:15:18.6289370Z [32mPASS: [36mhttps://github.com/dvolk/gnuplot.nim C                      [34m ( 1.42 sec)[0m
2020-04-11T13:15:18.6290280Z [32mPASS: [36mhttps://github.com/brentp/hts-nim C                         [34m ( 1.59 sec)[0m
2020-04-11T13:15:18.6291170Z [32mPASS: [36mhttps://github.com/johnnovak/illwill C                      [34m (17.38 sec)[0m
2020-04-11T13:15:18.6292080Z [32mPASS: [36mhttps://github.com/inim-repl/INim C                         [34m ( 3.19 sec)[0m
2020-04-11T13:15:18.6292980Z [32mPASS: [36mhttps://github.com/narimiran/itertools C                    [34m ( 2.03 sec)[0m
2020-04-11T13:15:18.6293870Z [32mPASS: [36mhttps://github.com/def-/iterutils C                         [34m ( 3.01 sec)[0m
2020-04-11T13:15:18.6294780Z [32mPASS: [36mhttps://github.com/LemonBoy/jstin C                         [34m ( 3.51 sec)[0m
2020-04-11T13:15:18.6295680Z [32mPASS: [36mhttps://github.com/pragmagic/karax C                        [34m (11.89 sec)[0m
2020-04-11T13:15:18.6296590Z [32mPASS: [36mhttps://github.com/numforge/loopfusion C                    [34m ( 2.15 sec)[0m
2020-04-11T13:15:18.6297480Z [32mPASS: [36mhttps://github.com/jangko/msgpack4nim C                     [34m (32.63 sec)[0m
2020-04-11T13:15:18.6298390Z [32mPASS: [36mhttps://github.com/fowlmouth/nake/ C                        [34m ( 1.93 sec)[0m
2020-04-11T13:15:18.6299270Z [32mPASS: [36mhttps://github.com/unicredit/neo C                          [34m ( 9.38 sec)[0m
2020-04-11T13:15:18.6300170Z [32mPASS: [36mhttps://github.com/icyphox/nicy C                           [34m ( 1.70 sec)[0m
2020-04-11T13:15:18.6300980Z [1m[31mFAIL: [36mhttps://github.com/trustable-code/NiGui C[0m
2020-04-11T13:15:18.6301920Z [1m[36mTest "https://github.com/trustable-code/NiGui" in category "nimble-packages"[0m
2020-04-11T13:15:18.6302650Z [1m[31mFailure: reBuildFailed[0m
2020-04-11T13:15:18.6302940Z package test failed
2020-04-11T13:15:18.6303630Z $ nim c -o:niguii -r src/nigui.nim

```
