Remove DATA_SEG_BITS.

Remove DATA_SEG_BITS.

The DATA_SEG_BITS hack was needed for older 32 bit platforms.
As a result of this change, Emacs won't work on IRIX 6.5 with IRIX
cc, but that platform is so old that SGI itself stopped supporting
it in December 2013.  If you still need Emacs on IRIX, please
either compile with GCC and port the undumping code, or run
'./configure --with-wide-int'.
* configure.ac (DATA_SEG_BITS): Remove.  All uses removed.
* src/alloc.c (gdb_make_enums_visible): Update to match lisp.h.
* src/lisp.h (GCTYPEBITS): Move definition up, and switch to the
DEFINE_GDB_SYMBOL_START way to define it.
(NONPOINTER_BITS): New macro.
(EMACS_INT): Use it.
[!USE_LSB_TAG && !WIDE_EMACS_INT]: Fail, and suggest reporting
the problem and/or configuring --with-wide-int.
(USE_LSB_TAG): Simplify, based on above changes.
(gdb_DATA_SEG_BITS): Remove.  All uses removed.
* src/vm-limit.c (exceeds_lisp_ptr): Remove.  All uses removed.