D56351 (included in LLVM 8.0.0) introduced "frame-pointer". All tests
which use "no-frame-pointer-elim" or "no-frame-pointer-elim-non-leaf"
have been migrated to use "frame-pointer".
Implement UpgradeFramePointerAttributes to upgrade the two obsoleted
function attributes for bitcode. Their semantics are ignored.
Differential Revision: https://reviews.llvm.org/D71863
Fangrui Song