Fix compile error for cygwin1.7.18, without -mwin32 option.

#263 occurd in CYGWIN_NT-6.1-WOW64 1.7.18(0.263/5/3) 2013-04-19 10:39 i686 Cygwin.

I think -mwin32 option isn't need in this version.
I remove and test. It's all green.