Nimble build linker and localdeps flags conflict
`nimble build -l:-static` and `nimble build --passL:-static` do different things. The former enables localdeps mode and the latter passes to the linker correctly. The problem is that the first case doesn't return an error and will cause confusion. I think a check that returns an error should be added for flags that don't support the `-flag:value` syntax. `nimble build --localdeps:foo` doesn't return an error either even though it should, at least in my opinion. Tested with `nimble v0.13.1`.