PGO: don't emit counter increment if no counters have been allocated.
PGO: don't emit counter increment if no counters have been allocated.

I hit this while debugging another issue where my sources were in an
inconsistent state, so I don't have a testcase. Regardless, this check is
simpler and more direct than checking if the option is enabled.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@203072 91177308-0d34-0410-b5e6-96231b3b80d8

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