ms Intrin.h: Fix __movsw's and __stosw's inline asm.

Before, clang's internal assembler would reject the inline asm in clang's
Intrin.h.  To make sure this doesn't happen for other Intrin.h functions using
__asm__ blocks, add 32-bit and 64-bit codegen tests for Intrin.h.

Sadly, these tests discovered that __readcr3 and __writecr3 have bad
implementations in 64-bit builds.  This will have to be fixed in a follow-up.

llvm-svn: 248234