[NFC] Simplify 'friend' declaration in ParsedAttr
[NFC] Simplify 'friend' declaration in ParsedAttr

As suggested in the post-commit review for D50531,
change from the templatized TrailingObjects friend declaration
to a version referring to the base.


git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@339382 91177308-0d34-0410-b5e6-96231b3b80d8

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