testsuite, Objective-C : Compatibility fixes.

Changes to deal with warnings and/or errors seen when compiling the
tests with clang.

gcc/testsuite/ChangeLog:

	* objc-obj-c++-shared/TestsuiteObject.h: If the compiler
	supports objc_root_object attributes, then mark the testsuite
	object accordingly.
	* objc-obj-c++-shared/TestsuiteObject.m: Avoid direct access
	to isa, which is an error for modern Objective-C.
	* objc/execute/class-tests-1.h: Declare a string function we
	use locally (avoid pulling in the whole of string.h).

gcc/testsuite/objc-obj-c++-shared/TestsuiteObject.h

@@ -24,6 +24,9 @@ along with GCC; see the file COPYING3.  If not see
 /* We use this root class instead of Object to keep the tests
    independent of the runtime being used.  Keep it simple.  */
 
+#if defined(__has_attribute) && __has_attribute(objc_root_class)
+__attribute__((objc_root_class))
+#endif
 @interface TestsuiteObject
 {
   Class isa;

gcc/testsuite/objc-obj-c++-shared/TestsuiteObject.m

@@ -64,6 +64,6 @@ along with GCC; see the file COPYING3.  If not see
 }
 - (const char *)name
 {
-  return class_getName (isa);
+  return object_getClassName (self);
 }
 @end

gcc/testsuite/objc/execute/class-tests-1.h

@@ -4,6 +4,8 @@
 #include <stdlib.h>
 #include "../../objc-obj-c++-shared/runtime.h"
 
+extern int strcmp(const char *, const char *);
+
 /*
  * Standard Tests For Classes and Objects - abort upon failing; return
  * normally if all is well.