Fix export of symbols to GDB.

Fix export of symbols to GDB.

* alloc.c (ARRAY_MARK_FLAG_VAL, PSEUDOVECTOR_FLAG_VAL, VALMASK_VAL)
(ARRAY_MARK_FLAG, PSEUDOVECTOR_FLAG, VALMASK): Move these here from
emacs.c, as this is a more-suitable home.  Had this been done earlier
the fix for 12036 would have avoided some of the problems noted in
<http://bugs.gnu.org/12036#13> by Eli Zaretskii, as the scope problems
would have been more obvious.
* emacs.c (gdb_CHECK_LISP_OBJECT_TYPE, gdb_DATA_SEG_BITS)
(gdb_GCTYPEBITS, gdb_USE_LSB_TAG)
(CHECK_LISP_OBJECT_TYPE, DATA_SEG_BITS, GCTYPEBITS, USE_LSB_TAG):
Remove; now done in lisp.h.
* lisp.h (PUBLISH_TO_GDB): New macro.
(GCTYPEBITS, USE_LSB_TAG, CHECK_LISP_OBJECT_TYPE, enum pvec_type)
(DATA_SEG_BITS): Use it.
(GCTYPEBITS, USE_LSB_TAG): Now also an enum, for GDB.
(CHECK_LISP_OBJECT_TYPE, DATA_SEG_BITS): Now just an enum, for GDB.
* mem-limits.h (EXCEEDS_LISP_PTR): Redo so that DATA_SEG_BITS need
not be usable in #if.  This simplifies things.