YCM build on Cygwin 64: errors in pyport.h, LONG_BIT wrong

I have still no luck in building YCM on cygwin64. Please see me comment in issue https://github.com/Valloric/YouCompleteMe/issues/66#issuecomment-27879120

I've tried some other flags (-DCMAKE_CXX_FLAGS=-m64) and compilers (mingw32/64, cygwin32/64) but was not successful.
