[driver] Add support for the COMPILER_PATH environment variable, which adds the specified path(s) to the list of prefix directories. rdar://10097714
[driver] Add support for the COMPILER_PATH environment variable, which adds the
specified path(s) to the list of prefix directories.
rdar://10097714

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@139677 91177308-0d34-0410-b5e6-96231b3b80d8

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