Revert "[PGO] Fix computation of function Hash"

This reverts commit 7c298c10.
Fails make check-clang.

Failing Tests (8):
	Clang :: Profile/c-counter-overflows.c
	Clang :: Profile/c-general.c
	Clang :: Profile/c-unprofiled-blocks.c
	Clang :: Profile/cxx-rangefor.cpp
	Clang :: Profile/cxx-throws.cpp
	Clang :: Profile/misexpect-switch-default.c
	Clang :: Profile/misexpect-switch-nonconst.c
	Clang :: Profile/misexpect-switch.c