Add an explanation of -Wobjc-literal-compare to the "Objective-C Literals" page
Add an explanation of -Wobjc-literal-compare to the "Objective-C Literals" page

(per Jean-Daniel's suggestion to keep around an explanation of why
direct comparisons on ObjC literals are a bad idea)

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@159972 91177308-0d34-0410-b5e6-96231b3b80d8

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