[codegen] toast silently ignores things it can't handle in `define` statements
followup for https://gitlab.com/kaushalmodi/nimterop-throwaway-1 

discussed here: https://gitter.im/nimgen/Lobby?at=5c4e8af8f46373406a10a9d1
note: i had to add (on OSX): `cIncludeDir("/opt/X11/include/")` in `eggx.nim`

adding to eggx.h
```c
void foobar();
#define foobar2 123
```

will indeed show those procs

nim c EGGX/eggx.nim
```
{.passC: "-I/private/tmp/d41/nimterop-throwaway-1/draw/EGGX080".}

{.passC: "-I/opt/X11/include/".}
Importing /private/tmp/d41/nimterop-throwaway-1/draw/EGGX080/eggx.h
/Users/timothee/git_clone/nim/nimterop/build/toast --pnim --preprocess --includeDirs+=/private/tmp/d41/nimterop-throwaway-1/draw/EGGX080 --includeDirs+=/opt/X11/include/ /private/tmp/d41/nimterop-throwaway-1/draw/EGGX080/eggx.h

{.experimental: "codeReordering".}
const
  headereggx = "/private/tmp/d41/nimterop-throwaway-1/draw/EGGX080/eggx.h"
  foobar2* = 123
proc foobar*() {.importc, header: headereggx.}
```

however the rest doesnt show anything; i think it's an instance of this:


[option to give error upon encountering `Potentially invalid syntax` · Issue #9 · genotrance/nimterop](https://github.com/genotrance/nimterop/issues/9)

which is getting fixed soon (now that plugin PR merged)

~~so probably the issue is that `eggx_ggetdisplayinfo`(etc) is not visible~~

EDIT:
~~so the type of `eggx_ggetdisplayinfo` is `int (int *, int *, int *)` and nimterop can't handle it, but instead of giving a warning (or error) it silently skips~~

EDIT
things that helped me debug this:
```
toast --past
toast --pnim
```
eg:
```
$nim_D/nimterop/build/toast --past --preprocess=true --defines+=FORCE --includeDirs+=/opt/X11/include/ --includeDirs+=EGGX080 /tmp/d41/nimterop-throwaway-1/draw/EGGX080/eggx.hq
```

- [ ] would also help if `--past` had an option to show name of symbol eg in `(preproc_arg 56 16 4)` => should also show symbol name