Fix two issues for profile staleness report.
1) It should be more accurate to use the sum of all entry count(`getHeadSamplesEstimate`) for the callsite samples than the total samples, since even the top-level callsite is mismatched, it does affect the inlining but it can still be merged into base profile and used later.
2) I accidentally missed to persist the num of mismatched callsite into binary.
Also added the asm testing to test the decoding of the section.
Reviewed By: hoy, wenlei
Differential Revision: https://reviews.llvm.org/D140063
97e2aeab71