Add _mm_prefetch and some others as MS builtins

This patch adds several built-ins that are required for ms 
compatibility. _mm_prefetch must be a built-in because it takes a 
compile-time constant argument and our prior approach of using a #define 
to the current built-in doesn't work in the presence of re-declaration 
of _mm_prefetch. The others can be obtained by including the windows 
system headers. If a user includes the windows system headers but not 
intrin.h they still need to work and therefore must be built-in because 
we don't get a chance to implement them in intrin.h in this case.

llvm-svn: 201734