Extend builtin fnspecs

Extend builtin fnspecs

	* attr-fnspec.h: Update toplevel comment.
	(attr_fnspec::attr_fnspec): New constructor.
	(attr_fnspec::arg_read_p,
	attr_fnspec::arg_written_p,
	attr_fnspec::arg_access_size_given_by_arg_p,
	attr_fnspec::arg_single_access_p
	attr_fnspec::loads_known_p
	attr_fnspec::stores_known_p,
	attr_fnspec::clobbers_errno_p): New member functions.
	(gimple_call_fnspec): Declare.
	(builtin_fnspec): Declare.
	* builtins.c: Include attr-fnspec.h
	(builtin_fnspec): New function.
	* builtins.def (BUILT_IN_MEMCPY): Do not specify RET1 fnspec.
	(BUILT_IN_MEMMOVE): Do not specify RET1 fnspec.
	(BUILT_IN_MEMSET): Do not specify RET1 fnspec.
	(BUILT_IN_STRCAT): Do not specify RET1 fnspec.
	(BUILT_IN_STRCPY): Do not specify RET1 fnspec.
	(BUILT_IN_STRNCAT): Do not specify RET1 fnspec.
	(BUILT_IN_STRNCPY): Do not specify RET1 fnspec.
	(BUILT_IN_MEMCPY_CHK): Do not specify RET1 fnspec.
	(BUILT_IN_MEMMOVE_CHK): Do not specify RET1 fnspec.
	(BUILT_IN_MEMSET_CHK): Do not specify RET1 fnspec.
	(BUILT_IN_STRCAT_CHK): Do not specify RET1 fnspec.
	(BUILT_IN_STRCPY_CHK): Do not specify RET1 fnspec.
	(BUILT_IN_STRNCAT_CHK): Do not specify RET1 fnspec.
	(BUILT_IN_STRNCPY_CHK): Do not specify RET1 fnspec.
	* gimple.c (gimple_call_fnspec): Return attr_fnspec.
	(gimple_call_arg_flags): Update.
	(gimple_call_return_flags): Update.
	* tree-ssa-alias.c (check_fnspec): New function.
	(ref_maybe_used_by_call_p_1): Use fnspec for builtin handling.
	(call_may_clobber_ref_p_1): Likewise.
	(attr_fnspec::verify): Update verifier.
	* calls.c (decl_fnspec): New function.
	(decl_return_flags): Use it.