I made some curious testing with the classic "swap bytes without a temp"
in OpenCL RC4. It seemed slightly faster on Kepler but slower on others.
Apparently Microsoft uses a different x64 calling convention. This is an
attempt to fix x86-64.S. We now use _WIN64 instead of __MINGW64__ in case
someone tries to do things with MSVC or anything else.
Unify MAYBE_INLINE definition with core john.
http://www.openwall.com/lists/john-dev/2013/10/29/2
john-descrypt-opencl-section0-fix.diff