Preprocessor: initialize member introduced in r173881.
Preprocessor: initialize member introduced in r173881.

Compilation always sets this explicitly, but creating a preprocessor
manually should still put the 'IsPreprocessedOutput' flag in a valid state.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@174077 91177308-0d34-0410-b5e6-96231b3b80d8

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