* gen-protos.c (overrides): New static local.
	(add_hash,parse_fn_proto): New static functions.
	(main): Add prototypes from SYS_PROTO_OVERRIDES to hash table before
	parsing sys-protos.h.  Reserve entry 0 in std_protos.
	* alpha/alpha.h (SYS_PROTO_OVERRIDES): Define.

From-SVN: r12598