Fix t-locale.c #define used to avoid a test when using mingw64

The macro __MINGW64_VERSION_MAJOR is defined even when mingw64 is being used to compile 32 bit versions of software with the -m32 switch.

__MINGW64__ is only defined while compiling 64 bit output.
Merge pull request #2 from KevinBrogan/master

Fix t-locale.c #define used to avoid a test when using mingw64