[PGO] Differentiate Clang instrumentation and IR level instrumentation profiles

This patch uses one bit in profile version to differentiate Clang
instrumentation and IR level instrumentation profiles.

PGOInstrumenation generates a COMDAT variable __llvm_profile_raw_version so
that the compiler runtime can set the right profile kind.
For Maco-O platform, we generate the variable as linkonce_odr linkage as
COMDAT is not supported.

PGOInstrumenation now checks this bit to make sure it's an IR level
instrumentation profile.

The patch was submitted as r260164 but reverted due to a Darwin test breakage.
Original Differential Revision: http://reviews.llvm.org/D15540

Differential Revision: http://reviews.llvm.org/D17020

llvm-svn: 260385