[clang][NFC] Adjust tests to not un/define predefined macros

An upcoming patch will be making all defining or undefining of
predefined macros to be warning (currently only some give a warning).
In preparation for this adjust some tests that would emit a warning:
 * In thread-specifier.c the undefine is done to avoid a different
   warning, but we get that warning just because __thread and
   __private_extern__ are the wrong way around so we can just swap
   them.
 * There are a couple of objective-c tests that redefine IBAction to
   what it's already defined as, so we can just remove the define.

clang/test/Sema/thread-specifier.c

@@ -6,11 +6,6 @@
 // RUN: %clang_cc1 -triple i686-pc-linux-gnu -fsyntax-only -Wno-private-extern -verify=expected,thread-local -pedantic -x c++ %s -DC11 -D__thread=_Thread_local -std=c++11 -Wno-deprecated
 // RUN: %clang_cc1 -triple i686-pc-linux-gnu -fsyntax-only -Wno-private-extern -verify=expected,thread-local -pedantic %s -std=c99 -D__thread=_Thread_local -DC99
 
-#ifdef __cplusplus
-// In C++, we define __private_extern__ to extern.
-#undef __private_extern__
-#endif
-
 __thread int t1; // thread-local-warning {{'_Thread_local' is a C11 extension}}
 __thread extern int t2; // thread-local-warning {{'_Thread_local' is a C11 extension}}
 __thread static int t3; // thread-local-warning {{'_Thread_local' is a C11 extension}}
@@ -19,7 +14,7 @@ __thread static int t3; // thread-local-warning {{'_Thread_local' is a C11 exten
 // expected-warning@-3 {{'__thread' before 'static'}}
 #endif
 
-__thread __private_extern__ int t4; // thread-local-warning {{'_Thread_local' is a C11 extension}}
+__private_extern__ __thread int t4; // thread-local-warning {{'_Thread_local' is a C11 extension}}
 struct t5 { __thread int x; }; // thread-local-warning {{'_Thread_local' is a C11 extension}}
 #ifdef __cplusplus
 // expected-error-re@-2 {{'{{__thread|_Thread_local|thread_local}}' is only allowed on variable declarations}}
@@ -47,7 +42,7 @@ int f(__thread int t7) { // expected-error {{' is only allowed on variable decla
 #endif
   extern __thread int t9; // thread-local-warning {{'_Thread_local' is a C11 extension}}
   static __thread int t10; // thread-local-warning {{'_Thread_local' is a C11 extension}}
-  __thread __private_extern__ int t11; // thread-local-warning {{'_Thread_local' is a C11 extension}}
+  __private_extern__ __thread int t11; // thread-local-warning {{'_Thread_local' is a C11 extension}}
 #if __cplusplus < 201103L
   __thread auto int t12a; // expected-error-re {{cannot combine with previous '{{__thread|_Thread_local}}' declaration specifier}} \
                           // thread-local-warning {{'_Thread_local' is a C11 extension}}

clang/test/SemaObjC/method-attributes.m

@@ -37,7 +37,6 @@ - (void) dep __attribute__((deprecated)) { } // OK private methodn
 
 
 // rdar://10529259
-#define IBAction void)__attribute__((ibaction)
 
 @interface Foo 
 - (void)doSomething1:(id)sender;

clang/test/SemaObjC/super-dealloc-attribute.m

@@ -87,7 +87,6 @@ + (void)registerClass:(id)name {
 @end
 
 // rdar://14251387
-#define IBAction void)__attribute__((ibaction)
 
 @interface UIViewController @end