Tweak X toolkit code to pacify modern GCC

Tweak X toolkit code to pacify modern GCC

* lwlib/lwlib-Xaw.c, lwlib/lwlib-Xm.c, lwlib/lwlib.c:
Don’t include <stdlib.h>, since this code now calls emacs_abort
rather than abort.
* lwlib/lwlib-Xaw.c (make_dialog, xaw_generic_callback)
(wm_delete_window):
* lwlib/lwlib-Xm.c (make_menu_in_widget, do_call):
* lwlib/lwlib.c (instantiate_widget_instance, lw_make_widget):
* lwlib/xlwmenu.c (abort_gracefully, draw_separator)
(separator_height, XlwMenuInitialize):
Use emacs_abort, not abort.  Without this change, some calls
to ‘abort’ were invalid, as stdlib.h was not always included.
* src/widget.c (resources, emacsFrameClassRec):
* src/xfns.c (x_window) [USE_X_TOOLKIT]:
* src/xmenu.c (create_and_show_popup_menu) [USE_X_TOOLKIT]:
* src/xterm.c (emacs_options) [USE_X_TOOLKIT}:
(x_term_init) [USE_X_TOOLKIT]:
Cast string constants to char * to pacify --enable-gcc-warnings.