cmake: Replace a bogus check for MSVC with WIN32

MSVC++ isn't the only compiler that targets Win32, and the file in
question is needed for all of them.
cmake: Replace another bogus check for MSVC with WIN32

Otherwise attempting to compile with any other compiler targeting Win32
results in build errors with the Lua code, unless (presumably) you are
targeting Cygwin or another full POSIX implementation on Win32.