Fix for MinGW build on Windows

GG_LONGLONG and GG_ULONGLONG shall use LL and ULL suffixes,
since MinGW is actuall a GCC compiler.

Solved by checking whether compilation happens with MinGW
or not using standard MinGW's __MINGW32__ and __MINGW64__
definitions.

Change-Id: I789b34f6342a56ba42f4b280f7242700022ab7a1