Fix bitcode auto-upgrade when using bitcode lazy loading

The auto-upgrade path could be called before the VST (global
names) was fully parsed, and thus intrinsic names were not
available and the autoupgrade logic could not operate.

Fix link failures with ThinLTO.

This is a recommit of r278610 with a different fix.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@278615 91177308-0d34-0410-b5e6-96231b3b80d8