Rename profile_rt.so to libprofile_rt.so under configure+make (it already was

under cmake).

Add libprofile_rt.a so that we can tell clang to link against it in --coverage
mode. Also turn it on by default in cmake builds.

Oscar, this touches a change you made for EXCLUDE_FROM_ALL support -- I think
I've done the right thing, but please let me know (or fix and commit) if not!

llvm-svn: 130470