compilation fix for cygwin

SSIA.

IMPORTANT NOTE, this fix is just for compilation, htop does not run properly on cygwin. :sob:
```
$ uname -a
CYGWIN_NT-6.1-WOW64 lynx 1.7.27(0.271/5/3) 2013-12-09 11:57 i686 Cygwin

$ ./htop.exe


htop 1.0.2 aborting. Unsupported platform.
Aborted (core dumped)
```