bug#18122: make error when configure --without-x

[martin rudalics <rudalics@gmx.at>]

> Moreover, it's just broken with --enable-gcc-warnings:
>
> ../../trunk/src/frame.c:371:1: error: no previous prototype for ‘frame_windows_min_size’ [-Werror=missing-prototypes]
>   frame_windows_min_size (Lisp_Object frame, Lisp_Object horizontal, Lisp_Object pixelwise)
>   ^
> ../../trunk/src/frame.c:413:1: error: no previous prototype for ‘adjust_frame_size’ [-Werror=missing-prototypes]
>   adjust_frame_size (struct frame *f, int new_width, int new_height, int inhibit, bool pretend)
>   ^
> ../../trunk/src/frame.c: In function ‘adjust_frame_size’:
> ../../trunk/src/frame.c:479:9: error: implicit declaration of function ‘FRAME_HAS_HORIZONTAL_SCROLL_BARS’ [-Werror=implicit-function-declaration]
>           : max (FRAME_TEXT_TO_PIXEL_HEIGHT (f, new_text_height),
>           ^
> cc1: all warnings being treated as errors
>
> And:
>
> ../../trunk/src/dispnew.c: In function ‘change_frame_size_1’:
> ../../trunk/src/dispnew.c:5509:7: error: implicit declaration of function ‘adjust_frame_size’ [-Werror=implicit-function-declaration]
>         adjust_frame_size (f, new_width, new_height, 5, pretend);
>         ^
> cc1: all warnings being treated as errors

Thanks for fixing this (I was about to check in a similar fix but
trunk was already locked by you).

martin