[ThinLTO] Use correct pipeline for ThinLTO in gold-plugin.

This change is the gold side of the change made in D17115 and clang
patch r261045 to add a ThinLTO specific pipeline that moves more of
the optimization to the backends.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@269386 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed