Based on ArchType, Clang's driver can select a non-Clang compiler.
String parsing in Clang would have sufficed if it were only that,
however this change anticipates true llvm support.
Differential Revision: http://reviews.llvm.org/D10413
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239631 91177308-0d34-0410-b5e6-96231b3b80d8
