SamplePGO - Sort samples by source location when emitting as text.

SamplePGO - Sort samples by source location when emitting as text.

When dumping function samples or writing them out as text format, it
helps if the samples are emitted sorted by source location. The sorting
of the maps is a bit slow, so we only do it on demand.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@253568 91177308-0d34-0410-b5e6-96231b3b80d8