Reapply "[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).

This reverts the revert commit beaf3d18. What's changed?

- I fixed up the covmap-V2 binary format tests using a linux VM.
- I updated the expected counts in instrprof-comdat.h to account for
  the fact that there have been bugfixes to clang coverage.
- I added an assert to make sure we don't get bitten by this again.

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

llvm-svn: 264641