Driver: Don't mix system tools with devtoolset tools on RHEL

For example, we don't want to mix a devtoolset gcc with system ld, because
they don't always work together.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/branches/release_40@304293 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed