Would you be able to get rid of this ```is_target_win32``` your on this case?

Essentially:
* Kill ```is_target_win32``` from d-lang.cc and ```d_gcc_is_target_win32``` from d-lang.cc and d-dmd-gcc.h
* Remove the ```IN_GCC``` and ```_WIN32``` macros from parse.c that uses ```d_gcc_is_target_win32``` and replace it with:
```
link = global.params.isWindows ? LINKwindows : LINKc;
```
* Add similar findCondition() conditions checking for ```OSX```, ```FreeBSD```, ```OpenBSD```, ```Solaris``` and ```linux```, and set the corresponding ```global.params.isXxxx``` values.

Thanks,
Iain