Mark _DYNAMIC to have attribute __weakref__, so that gcc-4 does not optimize

&_DYNAMIC == NULL away. From Matt Thomas.

lib/csu/common_elf/common.h

@@ -1,4 +1,4 @@
-/* $NetBSD: common.h,v 1.10 2004/08/26 20:57:47 thorpej Exp $ */
+/* $NetBSD: common.h,v 1.11 2006/05/17 17:08:07 christos Exp $ */
 
 /*
  * Copyright (c) 1995 Christopher G. Demetriou
@@ -81,7 +81,11 @@ void	_rtld_setup(void (*)(void), const Obj_Entry *obj);
  * if we happen to be compiling without -static but with without any
  * shared libs present, things will still work.
  */
-extern int _DYNAMIC;
+extern int _DYNAMIC
+#if __GNUC__ > 3
+    __attribute__((__weakref__))
+#endif
+    ;
 __weak_extern(_DYNAMIC);
 #endif /* DYNAMIC */