[InstrProfiling] Improve compile time when there is no work
[InstrProfiling] Improve compile time when there is no work

When there are no uses of profiling intrinsics in a module, and there's
no coverage data to lower, InstrProfiling has no work to do.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@323574 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit 472d76161ee69cf1c7b9ba570d184fd5a6d41544)

apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm