Re-enable Visual Studio Builds.

I tried to compile with Visual Studio using CMake and found these two sections of code 
causing problems for Visual Studio.  The first one removes the use of variable length 
arrays by instead using KMP_ALLOCA().  The second part eliminates a redundant cpuid 
assembly call by using the already existing __kmp_x86_cpuid() call instead.

llvm-svn: 240290