Miscellaneous fixes for non-default X toolkits.

Miscellaneous fixes for non-default X toolkits.
* configure.ac (MOTIF): Check for /usr/include/openmotif
and /usr/(lib|lib64)/openmotif if --with-x-toolkit=motif.
* lwlib/lwlib-Xm.c (make_menu_in_widget): Remove unused variable.
* src/xfns.c (Fx_file_dialog): Change to SSDATA to avoid warnings.
* src/xterm.c (x_frame_of_widget): Remove redundant prototype.
Move under #ifdef USE_LUCID.
(x_create_toolkit_scroll_bar): Adjust scroll_bar_name
definition and usage to avoid warnings.