Correctly testing for AVX support in x86 based off code from Hosts.cpp.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@180991 91177308-0d34-0410-b5e6-96231b3b80d8
Unbreaking the non-x86 build bots by protecting the AVX test code properly.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@180992 91177308-0d34-0410-b5e6-96231b3b80d8