Fix problems with 32-bit wide-int build exposed by MinGW

Fix problems with 32-bit wide-int build exposed by MinGW

 lisp.h (XPNTR): Move definition to after XTYPE, to avoid
 compilation error in an unoptimized build when !USE_LSB_TAG.
 src/w32heap.c (DUMPED_HEAP_SIZE): For 32-bit wide-int build, use the
 same larger value as for the 64-bit build.
 src/w32term.h (SCROLL_BAR_PACK): Cast the result to UINT_PTR to
 avoid compiler warnings.
 src/w32proc.c (Fw32_get_codepage_charset, Fw32_set_keyboard_layout):
 Avoid compiler warnings about cast from integer to pointer of
 different size.
 src/w32menu.c (menubar_selection_callback, w32_menu_show): Cast to
 UINT_PTR instead of EMACS_INT, to avoid compiler warnings about
 casting from integer to pointer of different size.
 (add_menu_item): Pass the help-echo string as a pointer to
 Lisp_String, not as a Lisp_Object.
 (w32_menu_display_help): Use make_lisp_ptr to reconstruct a Lisp
 string object from its C pointer.
 src/w32fns.c (w32_msg_pump) <WM_EMACS_UNREGISTER_HOT_KEY>: Use
 make_lisp_ptr instead of XIL, to reconstruct a Lisp_Cons from its
 C pointer.
 <WM_EMACS_TOGGLE_LOCK_KEY>: msg.lparam is now a C integer.
 (Fx_create_frame): Type-cast the result of XFASTINT to avoild
 compiler warnings about size differences.
 (Fw32_unregister_hot_key): Pass the tail of w32_grabbed_keys as a
 pointer to a Lisp_Cons struct, not as a disguised EMACS_INT.
 (Fw32_toggle_lock_key): Pass the new state of the key as a C
 integer; use -1 for nil.  Doc fix.
 src/.gdbinit (xgetsym): New subroutine.
 (xsymname, xsymbol): Use it.
 (xprintsym): No need to call xgetptr.