Mark all libobjc2 headers as system headers when not compiling the runtime

itself.  This makes clang hide warnings.

objc/Availability.h

@@ -1,3 +1,7 @@
+#if defined(__clang__) && !defined(__OBJC_RUNTIME_INTERNAL__)
+#pragma clang system_header
+#endif
+
 
 #ifdef STRICT_MACOS_X
 #	define OBJC_NONPORTABLE __attribute__((error("Function not supported by the Apple runtime")))

objc/Object.h

@@ -1,3 +1,7 @@
+#if defined(__clang__) && !defined(__OBJC_RUNTIME_INTERNAL__)
+#pragma clang system_header
+#endif
+
 #include <objc/runtime.h>
 
 @interface Object

objc/Protocol.h

@@ -1,3 +1,7 @@
+#if defined(__clang__) && !defined(__OBJC_RUNTIME_INTERNAL__)
+#pragma clang system_header
+#endif
+
 #import "Object.h"
 
 @interface Protocol : Object @end

objc/blocks_private.h

@@ -1,5 +1,9 @@
 #ifndef __LIBOBJC_BLOCKS_PRIVATE_H_INCLUDED__
 #define __LIBOBJC_BLOCKS_PRIVATE_H_INCLUDED__
+#if defined(__clang__) && !defined(__OBJC_RUNTIME_INTERNAL__)
+#pragma clang system_header
+#endif
+
 
 /*
  * This header file exposes some implementation details of the blocks runtime

objc/blocks_runtime.h

@@ -1,3 +1,7 @@
+#if defined(__clang__) && !defined(__OBJC_RUNTIME_INTERNAL__)
+#pragma clang system_header
+#endif
+
 /*
  * Blocks Runtime
  */

objc/capabilities.h

@@ -1,3 +1,7 @@
+#if defined(__clang__) && !defined(__OBJC_RUNTIME_INTERNAL__)
+#pragma clang system_header
+#endif
+
 /**
  * capabilities.h - This file defines the list of capabilities.  Runtime
  * capabilities can be checked.  You may use #ifdef to test at compile time

objc/developer.h

@@ -1,3 +1,7 @@
+#if defined(__clang__) && !defined(__OBJC_RUNTIME_INTERNAL__)
+#pragma clang system_header
+#endif
+
 enum objc_developer_mode_np
 {
 	/** User mode - the default. */

objc/encoding.h

@@ -1,3 +1,7 @@
+#if defined(__clang__) && !defined(__OBJC_RUNTIME_INTERNAL__)
+#pragma clang system_header
+#endif
+
 #ifndef __LIBOBJC_ENCODING_H_INCLUDED__
 #define __LIBOBJC_ENCODING_H_INCLUDED__
 

objc/hooks.h

@@ -1,3 +1,7 @@
+#if defined(__clang__) && !defined(__OBJC_RUNTIME_INTERNAL__)
+#pragma clang system_header
+#endif
+
 /**
  * This file includes all of the hooks that can be used to alter the behaviour
  * of the runtime.  

objc/message.h

@@ -1,3 +1,7 @@
+#if defined(__clang__) && !defined(__OBJC_RUNTIME_INTERNAL__)
+#pragma clang system_header
+#endif
+
 #ifndef _OBJC_MESSAGE_H_
 #define _OBJC_MESSAGE_H_
 
@@ -37,18 +41,8 @@ id objc_msgSend(id self, SEL _cmd, ...);
 #ifdef __cplusplus 
 id objc_msgSend_stret(id self, SEL _cmd, ...);
 #else
-// There is a bug in older versions of clang that incorrectly declares the
-// signature of this function as a builtin.
-#	ifdef __clang__
-#		if (__clang_major__ > 3) || ((__clang_major__ == 3) && __clang_minor__ >= 3)
-void objc_msgSend_stret(id self, SEL _cmd, ...);
-#		else
-id objc_msgSend_stret(id self, SEL _cmd, ...);
-#		endif
-#	else 
 void objc_msgSend_stret(id self, SEL _cmd, ...);
 #endif
-#endif
 /**
  * Standard message sending function.  This function must be cast to the
  * correct types for the function before use.  The first argument is the

objc/objc-api.h

@@ -1 +1,5 @@
+#if defined(__clang__) && !defined(__OBJC_RUNTIME_INTERNAL__)
+#pragma clang system_header
+#endif
+
 #include <objc/runtime.h>

objc/objc-arc.h

@@ -1,3 +1,7 @@
+#if defined(__clang__) && !defined(__OBJC_RUNTIME_INTERNAL__)
+#pragma clang system_header
+#endif
+
 #ifndef __OBJC_ARC_INCLUDED__
 #define __OBJC_ARC_INCLUDED__
 /**

objc/objc-auto.h

@@ -1,3 +1,7 @@
+#if defined(__clang__) && !defined(__OBJC_RUNTIME_INTERNAL__)
+#pragma clang system_header
+#endif
+
 /**
  * objc-auto.h - This file provides the interface for Objective-C garbage
  * collection

objc/runtime-deprecated.h

@@ -1,3 +1,7 @@
+#if defined(__clang__) && !defined(__OBJC_RUNTIME_INTERNAL__)
+#pragma clang system_header
+#endif
+
 #if !defined(__GNUSTEP_LIBOBJC_RUNTIME_DEPRECATED_INCLUDED__) && !defined(GNUSTEP_LIBOBJC_NO_LEGACY)
 #	define __GNUSTEP_LIBOBJC_RUNTIME_DEPRECATED_INCLUDED__
 

objc/runtime.h

@@ -1,3 +1,7 @@
+#if defined(__clang__) && !defined(__OBJC_RUNTIME_INTERNAL__)
+#pragma clang system_header
+#endif
+
 #ifndef __LIBOBJC_RUNTIME_H_INCLUDED__
 #define __LIBOBJC_RUNTIME_H_INCLUDED__
 

objc/slot.h

@@ -1,3 +1,7 @@
+#if defined(__clang__) && !defined(__OBJC_RUNTIME_INTERNAL__)
+#pragma clang system_header
+#endif
+
 #ifndef __OBJC_SLOT_H_INCLUDED__
 #define __OBJC_SLOT_H_INCLUDED__
 /**