Work around overloading bug in MSVC 2015
Work around overloading bug in MSVC 2015

MSVC 2015 appears to be unable to find the correct operator== here. I
haven't yet filed a bug with Microsoft as I've been unable to create a
reduced test case.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@237862 91177308-0d34-0410-b5e6-96231b3b80d8

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