Align perf reader to fdata behavior by sorting BranchData after reading samples,
in the same way as DataReader:
20c66a0c66/bolt/lib/Profile/DataReader.cpp (L1239)
Namely, that order affects CallSiteInfo annotations which determine the
construction order of CallGraph, which in turn affects function reordering.
Reviewed By: #bolt, rafauler
Differential Revision: https://reviews.llvm.org/D152731