This is to avoid the need to update a bunch of test files when the PGO
instrumentation function hashing changes.
Split off of D84782.
Differential Revision: https://reviews.llvm.org/D84865
Add an option to always instrument function entry BB (default off)
Add an option to do atomically updates on the first counter in each
instrumented function.
Differential Revision: https://reviews.llvm.org/D82123