Work around a bug in clang 3.1 that declares objc_msgSend_stret as a builtin

with the wrong signature.

objc/message.h

@@ -37,7 +37,17 @@ 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__ >= 2)
 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

objc_msgSend.x86-64.S

@@ -95,7 +95,7 @@
 	push  %rsi                           # Save self where it can be modified
 	mov   %rsp, %rdi
 	push  %rdx
-	mov   %rdx, %rsi                     # move _cmd to where the callee expects it to be
+	mov   %rdx, %rsi                     # move _cmd to where the callee expects it to be
 .endif
 
 	.cfi_adjust_cfa_offset 0xD8