Add some hash_map_safe_* functions like vec_safe_*.

Add some hash_map_safe_* functions like vec_safe_*.

gcc/
	* hash-map.h (default_hash_map_size): New variable.
	(create_ggc): Use it as default argument.
	(hash_map_maybe_create, hash_map_safe_get)
	(hash_map_safe_get_or_insert, hash_map_safe_put): New fns.
gcc/cp/
	* constexpr.c (maybe_initialize_fundef_copies_table): Remove.
	(get_fundef_copy): Use hash_map_safe_get_or_insert.
	* cp-objcp-common.c (cp_get_debug_type): Use hash_map_safe_*.
	* decl.c (store_decomp_type): Remove.
	(cp_finish_decomp): Use hash_map_safe_put.
	* init.c (get_nsdmi): Use hash_map_safe_*.
	* pt.c (store_defaulted_ttp, lookup_defaulted_ttp): Remove.
	(add_defaults_to_ttp): Use hash_map_safe_*.

From-SVN: r276484