Fairly major surgery to RewriteTest::SynthesizeObjcInternalStruct().

Fairly major surgery to RewriteTest::SynthesizeObjcInternalStruct().

This allows us to handle funky stuff like...

#if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_3
@interface NSLayoutManager : NSObject <NSCoding, NSGlyphStorage> {
#else /* MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_3 */
@interface NSLayoutManager : NSObject <NSCoding> {
#endif /* MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_3 */

...which now rewrites to...

#if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_3
#ifndef _REWRITER_typedef_NSLayoutManager
#define _REWRITER_typedef_NSLayoutManager
typedef struct objc_object NSLayoutManager;
#endif

struct NSLayoutManager {
    struct NSObject _NSObject;

#else /* MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_3 */
// @interface NSLayoutManager : NSObject <NSCoding> {
#endif /* MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_3 */

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@44129 91177308-0d34-0410-b5e6-96231b3b80d8