Verify that llvm can generate the prefetchw instruction when the CPU is
Atom Silvermont.

Patch by Sriram Murali.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190957 91177308-0d34-0410-b5e6-96231b3b80d8
Attempt to fix llvm-ppc64-linux2 buildbot failure by adding
-march=x86 to SLM test.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190958 91177308-0d34-0410-b5e6-96231b3b80d8