* cppinit.c (struct lang_flags): Rename trigraphs std.
	(set_lang): Update.
	* cpplib.h (struct cpp_options): New member std.
	* cppmacro.c (_cpp_builtin_macro_text): Use std.
	(collect_args): Flag whether to swallow a possible future
	comma pasted with varargs.
	(replace_args): Use this flag.
	* doc/cpp.texi: Update varargs extension documentation.
testsuite:
	* gcc.dg/cpp/vararg3.c, gcc.dg/cpp/vararg4.c: New tests.

From-SVN: r56077