dumb down our CPP so that it works in both traditional and ansi modes

Same idea as my recent OpenGLRaw pull request.

This time I used sed:

```
sed -i '' -E 's/(API_ENTRY[^\(]*\()([^,]*),/\1dyn_\2,ptr_\2,\2,/;' src/**/*.hs
```

Note that probably won't work on GNU sed.