testsuite, Objective-C : Fix call-super-2.m for newer NeXT headers.

We were using a callout to runtime.h which, eventually brings in the system
runtime.h.  One newer versions of the Darwin/NeXT headers this declares the
objc_getClass() function as returning Class, rather than the internal
representation of that.  This breaks a fragile assumption in objc-act that
the use of these internal functions can be deduced by looking at the function
type.  Ultimately, the fragility should be fixed - but this fixes up the test
so that it only uses the compiler's forward declaration of the function.

gcc/testsuite/ChangeLog:

	* objc.dg/call-super-2.m: Remove inclusion of runtime.h.
	Add a FIXME about the test portability.

gcc/testsuite/objc.dg/call-super-2.m

@@ -3,7 +3,8 @@
 /* { dg-do compile } */
 
 #include "../objc-obj-c++-shared/TestsuiteObject.h"
-#include "../objc-obj-c++-shared/runtime.h"
+/* NOTE: we are relying on the built-in type for objc_getClass being used
+   rather than the one that might come from including <objc/runtime.h>.  */
 #include <stddef.h>
 
 /* FIXME: This is temporary.  At the moment, the compiler, when
@@ -14,6 +15,9 @@
 # define objc_getClass(C) objc_get_class(C)
 #endif
 
+/* FIXME: casting of super is not permitted by clang, so that many of the
+   tests here are testing non-portable code.  */
+
 @protocol Func
 + (int) class_func0;
 - (int) instance_func0;