[BOLT] Fix ICF non-determinism in non-relocation mode

Summary:
ICF may fold functions in arbitrary order when running multi-threaded.
This is fine in relocation mode as we end up with just one function
holding all function symbols.

However, in non-relocation mode we keep all function bodies, and if we
keep merging profiles in non-deterministic order, we end up with
functions with non deterministic profiles. The fix for non-relocation
mode is to not merge profiles as the factual new profile could be
different from the merged one since both function instances are
potentially callable.

Additionally, emit extra symbols for ICF functions in non-relocation
mode to make it possible to track the folding.

(cherry picked from FBD20889866)