[SubtargetFeatures] Don't call ApplyFeatureFlag if the feature name is '+help'
[SubtargetFeatures] Don't call ApplyFeatureFlag if the feature name is '+help'

Just print the help and stop. Otherwise we'll print a message about it not being a real feature name after printing the help text.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@355299 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm