* builtins.def (BUILT_IN_VA_ARG_PACK_LEN): New builtin.
* builtins.c (expand_builtin) <case BUILT_IN_VA_ARG_PACK_LEN>: Issue
error if __builtin_va_arg_pack_len () wasn't optimized out during
inlining.
* tree-inline.c (copy_bb): Replace __builtin_va_arg_pack_len ()
with the number of inline's anonymous arguments.
* doc/extend.texi: Document __builtin_va_arg_pack_len ().
* gcc.dg/va-arg-pack-len-1.c: New test.
* g++.dg/va-arg-pack-len-1.C: New test.
From-SVN: r128376
