Re-apply https://reviews.llvm.org/D87921, was reverted to triage a PPC bot failure.

D87921 was reverted in commit b89059a3
as it was causing an unknown llvm PPC bot failure.  Reapplying the patch
after confirming that this is not responsible. Build bot failure:
https://reviews.llvm.org/D87921#2286644  which caused the revert.

The wrong placement of add pass with optimizations led to
-funique-internal-linkage-names being disabled.

Fixed the placement of the MPM.addpass for UniqueInternalLinkageNames to make it
work correctly with -O2 and new pass manager. Updated the tests to explicitly
check O0 and O1.

Differential Revision: https://reviews.llvm.org/D87921