InstrProf: Set profile data to visibility hidden

Shared objects are fairly broken for InstrProf right now -- a follow-up
commit in compiler-rt will fix the rest of this.

The main problem here is that at link time, profile data symbols in the
shared object might get used instead of symbols from the main
executable, creating invalid profile data sections.

<rdar://problem/16918688>

llvm-svn: 208939