Temporarily revert r176116 for compile-time performance regression.

This reverts commit ea95e4587fd13606fbf63b10a07a7d02026aa39c.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@176151 91177308-0d34-0410-b5e6-96231b3b80d8