isystem: ship and use stdarg.h

Ship minimal stdarg.h (1 type, 4 macros) as <linux/stdarg.h>.
stdarg.h is the only userspace header commonly used in the kernel.

GPL 2 version of <stdarg.h> can be extracted from
http://archive.debian.org/debian/pool/main/g/gcc-4.2/gcc-4.2_4.2.4.orig.tar.gz

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
diff --git a/lib/kasprintf.c b/lib/kasprintf.c
index bacf7b8..cd2f597 100644
--- a/lib/kasprintf.c
+++ b/lib/kasprintf.c
@@ -5,7 +5,7 @@
  *  Copyright (C) 1991, 1992  Linus Torvalds
  */
 
-#include <stdarg.h>
+#include <linux/stdarg.h>
 #include <linux/export.h>
 #include <linux/slab.h>
 #include <linux/types.h>