since it is impossible to distinguish unpromoted types from small
(struct) types. Renamed __va_promote() to __va_size() since it is
related to sizes of args on the stack and not to promotion.
PR: 3884
Submitted by: mostly by arnej@math.ntnu.no (Arne Henrik Juul)
Obtained from: name of__va_size and some parentheses fixes from NetBSD