clang/lib/Basic/FileManager.cpp: Detect the root directory with PathV2. It should be better fix for PR10331, or, "clang X:\foo.c" fails.
clang/lib/Basic/FileManager.cpp: Detect the root directory with PathV2. It should be better fix for PR10331, or, "clang X:\foo.c" fails.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@158596 91177308-0d34-0410-b5e6-96231b3b80d8

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