PGO: rename FileCheck variable to follow the existing convention.

I added this "STF" variable without noticing that all the other counter names
end with a "C". Renaming it to "STC" for consistency.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@203165 91177308-0d34-0410-b5e6-96231b3b80d8
PGO: rename profile data files from .pgodata to .profdata.

These tests were added before we had settled on using a .profdata extension
for the profile data files. Renaming them now for consistency.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@203166 91177308-0d34-0410-b5e6-96231b3b80d8