[llvm-profdata] Don't treat non-fatal merge errors as fatal

This fixes an issue seen on the coverage bot:
http://lab.llvm.org:8080/green/view/Experimental/job/clang-stage2-coverage-R/1930

Profile merging shouldn't fail if a single counter mismatch is detected.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@318555 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed