Clarify the LibTooling.rst a bit
Clarify the LibTooling.rst a bit

The ClangCheck tool has changed and no longer is exactly equivalent to the
code pasted in the doc.


git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@199215 91177308-0d34-0410-b5e6-96231b3b80d8

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