[Coverage] Fix the way we load "<unknown>:func" records

When emitting coverage mappings for functions with local linkage and an
unknown filename, we use "<unknown>:func" for the PGO function name. The
problem is that we don't strip "<unknown>" from the name when loading
coverage data, like we do for other file names. Fix that and add a test.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@264559 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed