SamplePGO - Do not count never-executed inlined functions when computing coverage.

If a function was originally inlined but not actually hot at runtime,
its samples will not be counted inside the parent function. This throws
off the coverage calculation because it expects to find more used
records than it should.

Fixed by ignoring functions that will not be inlined into the parent.
Currently, this is inlined functions with 0 samples.  In subsequent
patches, I'll change this to mean "cold" functions.

llvm-svn: 253716