[PGO] Stop using invalid char in instr variable names.

Before the patch, -fprofile-instr-generate compile will fail
if no integrated-as is specified when the file contains
any static functions (the -S output is also invalid).

This is the second try. The fix in this patch is very localized.
Only profile symbol names of profile symbols with internal 
linkage are fixed up while initializer of name syms are not 
changes. This means there is no format change nor version bump.

llvm-svn: 255434