Fix sfence, lfence, mfence, and clflush to be able to be selected when AVX is enabled...

Fix sfence, lfence, mfence, and clflush to be able to be selected when AVX is enabled. Fix monitor and mwait to require SSE3 or AVX, previously they worked even if SSE3 was disabled. Make prefetch instructions not set the execution domain since they don't use XMM registers.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@147409 91177308-0d34-0410-b5e6-96231b3b80d8