* lisp/window-x.el (merge-frames, split-frame): New commands.

Fixes bug#79581
Copyright-paperwork-exempt: yes

* src/lisp.h: Include <sys-limits.h>.
(MAX_RW_COUNT): Remove, as it is the same thing as sys-limits.h’s
SYS_BUFSIZE_MAX.  All uses replaced by SYS_BUFSIZE_MAX.

* src/emacs.c (read_full):
Simplify by assuming MAX_RW_COUNT is defined.
* src/lisp.h (MAX_RW_COUNT): Move here from src/sysdep.c.
* src/pdumper.c (dump_read_all):
Use MAX_RW_COUNT rather than defining our own equivalent.

* src/pdumper.c (dump_builtin_symbol_p): Test BARE_SYMBOL_P
\(object) rather than SYMBOLP to avoid depending on the value of
symbols_with_pos_enabled or depositing non-relocated references
to vectorlikes in the dump file.  Clarify commentary.

* src/pdumper.c (dump_fwd_int, dump_fwd_bool, dump_fwd_obj): Do
not redundantly dump constant forwarding descriptors; restrict
to dumping the objects being forwarded to.
(dump_fwd_buffer_obj): Copy from the dump file into bss rather
than load buffer forwarding descriptors from the dump file
itself.
(dump_fwd_kboard_obj): Delete function.
(dump_fwd): Don't return offset of dumped objects.
(dump_blv): Adjust correspondingly.
(dump_pre_dump_symbol): Improve documentation.  Record offset of
forwarding objects in relation to `emacs_basis' rather than the
dump file.
(dump_symbol): Restore forwarding descriptors to their original
values as static variables in Emacs.  This reduces the size of
dump files by an insignificant 2kb but facilitates certain kinds
of watchpoints on platforms where ASLR cannot be disabled, e.g.,
Android.

* src/pdumper.c (VM_SUPPORTED): Don't define to 0 when
!USE_LSB_TAG if WIDE_EMACS_INT.

* src/lisp.h (USE_LSB_TAG):

* src/pdumper.c (pdumper_load): Correct typos in commentary and
error messages.