Fix a regression introduced by r131955 which broke #include_next in subtle situations because the Angled directories and the System directories were not being uniqued  together, breaking #include_next.  I'll see about a testcase, but it will be insane.
Fix a regression introduced by r131955 which broke #include_next in subtle situations
because the Angled directories and the System directories were not being uniqued 
together, breaking #include_next.  I'll see about a testcase, but it will be insane.


git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@133212 91177308-0d34-0410-b5e6-96231b3b80d8

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