Summary: x86 is not a valid arch for target triples, but x86_64 and i386 are.

Reviewers: rengolin, silvas

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D26960

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@288723 91177308-0d34-0410-b5e6-96231b3b80d8