Support for reading run counts in llvm-cov.

This patch enables llvm-cov to correctly output the run count stored in
the GCDA file. GCOVProfiling currently does not generate this
information, so the GCDA run data had to be hacked on from a GCDA file
generated by gcc. This is corrected by a subsequent patch.

With the run and program data included, both llvm-cov and gcov produced
the same output.