PGO: Substitute pid for %p in filename

Add logic to do a printf-style substitution of %p for the process pid in
the filename.

It's getting increasingly awkward to work on lib/profile without test
infrastructure.  This needs to be fixed!

<rdar://problem/16383358>

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@204414 91177308-0d34-0410-b5e6-96231b3b80d8