[arcmt] Find out whether there is an ARC runtime directly from the triple, avoid hacky delegation to the driver for that.
[arcmt] Find out whether there is an ARC runtime directly from the triple, avoid hacky delegation to the driver for that.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@133464 91177308-0d34-0410-b5e6-96231b3b80d8

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