[NFC][interop] rename the PrintAsObjC library to PrintAsClang

We're starting to support emission of C++ header interfaces, so a language-agnostic name makes more sense

include/swift/PrintAsClang/PrintAsClang.h

@@ -0,0 +1,36 @@
+//===--- PrintAsClang.h - Emit a header file for a Swift AST ----*- C++ -*-===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SWIFT_PRINTASCLANG_H
+#define SWIFT_PRINTASCLANG_H
+
+#include "swift/Basic/LLVM.h"
+#include "swift/AST/AttrKind.h"
+#include "swift/AST/Identifier.h"
+
+namespace swift {
+  class ModuleDecl;
+  class ValueDecl;
+
+  /// Print the Objective-C-compatible declarations in a module as a Clang
+  /// header.
+  ///
+  /// Returns true on error.
+  bool printAsObjC(raw_ostream &out, ModuleDecl *M, StringRef bridgingHeader);
+
+  /// Print the C++-compatible declarations in a module as a Clang header.
+  ///
+  /// Returns true on error.
+  bool printAsCXX(raw_ostream &os, ModuleDecl *M);
+}
+
+#endif