[lit] When setting SDKROOT on Darwin, use '--sdk macosx' to find the right SDK path.
[lit] When setting SDKROOT on Darwin, use '--sdk macosx' to find the right SDK path.

This will make sure that we find an actual path in case you have Command Line Tools installed.



git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@287403 91177308-0d34-0410-b5e6-96231b3b80d8

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