Constify a functor's function call operator because it can/should be.
Constify a functor's function call operator because it can/should be.

Patch by Graham Lee (graham@iamleeg.com)!

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@218385 91177308-0d34-0410-b5e6-96231b3b80d8

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