[PGO] test case cleanups

1. Make test case more focused and robust by focusing on what to be tested (linkage, icall) -- make it easier to validate
2. Testing linkages of data and counter variables instead of names. Counters and data are more relavant to be tested.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@259067 91177308-0d34-0410-b5e6-96231b3b80d8