Index: sys/sys/_stdarg.h
===================================================================
--- sys/sys/_stdarg.h
+++ sys/sys/_stdarg.h
@@ -42,7 +42,7 @@
   typedef __va_list       va_list;
 #endif
 
-#ifdef __GNUCLIKE_BUILTIN_STDARG
+#if defined(__GNUCLIKE_BUILTIN_STDARG) && !defined(va_start)
   #define	va_start(ap, last)	__builtin_va_start((ap), (last))
   #define	va_arg(ap, type)	__builtin_va_arg((ap), type)
   #define	__va_copy(dest, src)	__builtin_va_copy((dest), (src))