decay_conversion converts a bit-field access to its declared type, which
isn't what we want here; it even has a comment that the caller is expected
to have already used default_conversion to perform integral promotion.  This
function handles arithmetic promotion differently, but we still don't want
to call decay_conversion before that happens.

	* call.c (convert_arg_to_ellipsis): Don't call decay_conversion for
	arithmetic arguments.

From-SVN: r276059