Reapply (2x) "[PGO] Fix name encoding for ObjC-like functions"

Function names in ObjC can have spaces in them. This interacts poorly
with name compression, which uses spaces to separate PGO names. Fix the
issue by using a different separator and update a test.

I chose "\01" as the separator because 1) it's non-printable, 2) we
strip it from PGO names, and 3) it's the next natural choice once "\00"
is discarded (that one's overloaded).

What's changed since the original commit?

- I fixed up the covmap-V2 binary format tests using a linux VM.
- I weakened the CHECK lines in instrprof-comdat.h to account for the
  fact that there have been bugfixes to clang coverage. These will be
  fixed up in a follow-up.
- I added an assert to make sure we don't get bitten by this again.
- I constructed the c-general.profraw file without name compression
  enabled to appease some bots.

Differential Revision: http://reviews.llvm.org/D18516

llvm-svn: 264658