PGO: rename FileCheck variable to follow the existing convention.
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: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@203165 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang