bug#16930: [ac02f3a7] fails to build without HAVE_WINDOW_SYSTEM

[Eli Zaretskii]

> From: Ivan Shmakov <ivan@siamics.net>
> Date: Mon, 03 Mar 2014 19:29:39 +0000
> 
> ../../src/font.c: In function 'Fframe_font_cache':
> ../../src/font.c:4853:3: error: implicit declaration of function 
> 'FRAME_DISPLAY_INFO' [-Werror=implicit-function-declaration]
>    return FRAME_DISPLAY_INFO (decode_live_frame (frame))->name_list_element;
>    ^
> ../../src/font.c:4853:56: error: invalid type argument of '->' (have 'int')
>    return FRAME_DISPLAY_INFO (decode_live_frame (frame))->name_list_element;
>                                                         ^
> ../../src/font.c:4854:1: error: control reaches end of non-void function 
> [-Werror=return-type]
>  }
>  ^
> cc1: all warnings being treated as errors
> make[1]: *** [font.o] Error 1

Should be fixed now (trunk revision 116646).

>       As all the other invocations of FRAME_DISPLAY_INFO () seem to be
>       guarded with #ifdef HAVE_WINDOW_SYSTEM, I’d rather assume that
>       the whole DEFUN ("frame-font-cache", …) should also be within
>       such guards, along with the reference to Sframe_font_cache
>       within syms_of_font ().

No, it's not enough to #ifdef away that function when
HAVE_WINDOW_SYSTEM is not defined, because if HAVE_WINDOW_SYSTEM _is_
defined, you can still call the function for a TTY frame.

In general, one has always think about multi-tty when handling such
issues: a build that supports window-system can have frames that
don't.  It's no longer a compile-time issue.