Support const and noreturn DEFUN attributes.

Support const and noreturn DEFUN attributes.

* lib-src/make-docfile.c (struct global): New field 'flags'.
(DEFUN_noreturn, DEFUN_const): New enum bitfields.
(add_global): Now return pointer to global.
(write_globals): Add _Noreturn and ATTRIBUTE_CONST attributes
if requested by global's flags.
(stream_match): New function.
(scan_c_stream): Recognize 'attributes:' of DEFUN.

* src/callint.c (Finteractive):
* src/character.c (Fcharacterp, Fmax_char):
* src.data.c (Feq, Fnull, Fconsp, Fatom, Flistp, Fnlistp, Fsymbolp)
(Fstringp, Fchar_or_string_p, Fintegerp, Fnatnump, Fnumberp)
(Ffloatp, Fbyteorder):
* src/decompress.c (Fzlib_available_p):
* src/fns.c (Fidentity):
* src/frame.c (Fframe_windows_min_size):
* src/gnutls.c (Fgnutls_error_p, Fgnutls_available_p):
* src/window.c (Fwindow__sanitize_window_sizes):
* src/xdisp.c (Ftool_bar_height):
* src/xfaces.c (Fface_attribute_relative_p): Add const attribute.
* src/emacs.c (Fkill_emacs):
* src/eval.c (Fthrow):
* src/keyboard.c (Ftop_level, Fexit_recursive_edit)
(Fabor_recursive_edit): Add noreturn attribute.