* configure.ac (ALIGNOF_INT, ALIGNOF_LONG, ALIGNOF_LONG_LONG):
New variables.
(emacs_cv_alignas_unavailable): Define if alignas and structure
alignment primitives are unavailable.  In such an environment,
the MSB tagging scheme must be enabled, as must the GNU malloc.

* msdos/sed2v2.inp: Adjust correspondingly.

* src/alloc.c (union emacs_align_type): Remove types which
contain flexible array members.  The address of a field
subsequent to an aggregate with flexible array members cannot
validly be taken.
(mark_memory) [!USE_LSB_TAG && !WIDE_EMACS_INT]: Strip type bits
before scanning memory.

* src/emacs.c (main):

* src/eval.c (Fautoload_do_load):

* src/fns.c (Frequire): Rename a number of illogically named
fields.

* src/lisp.h (ALIGNOF_EMACS_INT): Define to the natural
alignment of EMACS_INT.
(IDEAL_GCALIGNMENT): New macro.
(USE_LSB_TAG): Disable if no alignment specifiers are available,
WIDE_EMACS_INT is undefined, and the natural alignment of
EMACS_INT falls short of LSB tagging's requirements.
(gflags): Rename illogically named fields and don't define them
as bitfields, which runs afoul of certain compiler issues.
(will_dump_p, will_bootstrap_p, will_dump_with_pdumper_p)
(dumped_with_pdumper_p): Adjust accordingly.

* src/pdumper.c (VM_SUPPORTED): Define to 0 when !USE_LSB_TAG.
It is better to read dump files into the heap by hand than to be
supplied with an address that is not representable.
(_dump_object_start_pseudovector): Rename to
dump_object_start_pseudovector, to avoid encroaching on reserved
names.
(START_DUMP_PVEC): Adjust correspondingly.
(dump_mmap_contiguous_vm): Preserve errno around failure
cleanup.
(dump_bitset_bit_set_p): Work around certain compiler issues.
(pdumper_load) [!USE_LSB_TAG]: Reject dump file allocations
that are not representable as Lisp_Objects.

Tested on i386-unknown-solaris2.10, sparc-sun-solaris2.10.

Prompted by a private email from Pip Cet.

* src/alloc.c (pointer_align): Only define if
!USE_ALIGNED_ALLOC.

* src/alloc.c (make_formatted_string):
Grow the local buffer from 64 to MAX_ALLOCA bytes.

From a suggestion by Pip Cet.
* src/alloc.c (make_formatted_string): Omit first argument,
to simplify the calling convention.  All callers changed.
* src/doprnt.c (doprnt): Also support %u.  Update doc.

The case_Lisp_Int macro was originally introduced with different
definitions depending on USE_2_TAGS_FOR_INTS.  However, since commit
2b5701247845, we have assumed that USE_2_TAGS_FOR_INTS is always
defined, and the macro has only a single definition.  As a result, the
macro is now unnecessary, and replacing it with standard C case labels
improves readability and understanding.

* src/lisp.h (case_Lisp_Int): Delete macro.
* src/alloc.c (process_mark_stack, survives_gc_p):
* src/data.c (Fcl_type_of):
* src/fns.c (value_cmp, sxhash_obj):
* src/pdumper.c (dump_object):
* src/print.c (print_object):
* src/xfaces.c (face_attr_equal_p): Remove uses of above macro.

Since the introduction of the 'calln' macro, the 'call1', 'call2', ...,
'call8' macros are just aliases for the former.  This is slightly
misleading and potentially unhelpful.  The number of arguments N can
also easily go out-of-synch with the used alias callN.  There is no
reason not to replace these aliases with using 'calln' directly.

To reduce the risk for mistakes, the tool Coccinelle was used to make
these changes.  See <https://coccinelle.gitlabpages.inria.fr/website/>.

* src/alloc.c, src/androidvfs.c, src/androidfns.c, src/buffer.c:
* src/callint.c, src/callproc.c, src/casefiddle.c, src/charset.c:
* src/chartab.c, src/cmds.c, src/coding.c, src/composite.c:
* src/data.c, src/dbusbind.c, src/dired.c, src/doc.c:
* src/emacs.c, src/eval.c, src/fileio.c, src/filelock.c:
* src/fns.c, src/frame.c, src/gtkutil.c, src/haikufns.c:
* src/haikumenu.c, src/image.c, src/insdel.c, src/intervals.c:
* src/keyboard.c, src/keymap.c, src/lisp.h, src/lread.c:
* src/minibuf.c, src/nsfns.m, src/nsselect.m, src/pgtkfns.c:
* src/pgtkselect.c, src/print.c, src/process.c, src/sort.c:
* src/syntax.c, src/textconv.c, src/textprop.c, src/undo.c:
* src/w32fns.c, src/window.c, src/xfaces.c, src/xfns.c:
* src/xmenu.c, src/xselect.c, src/xterm.c:
Replace all uses of 'call1', 'call2', ..., 'call8' with 'calln'.

Problem reported by Hong Xu <https://bugs.gnu.org/75551#14>.
* src/alloc.c (MALLOC_IS_LISP_ALIGNED): static_assert it,
since it is true on all current Emacs platforms.
All uses simplified to assume it is true.
(xmalloc, xzalloc, xrealloc, lisp_malloc): Just use
malloc/calloc/realloc.  Since we are using the malloc-gnu
and realloc-posix modules, we need not worry about whether
these functions return a null pointer for zero-size requests.
(xrealloc): Stop worrying about no-longer-existing platforms
where realloc (nullptr, ...) did not work.
(laligned, lmalloc, lrealloc): Remove.  All uses removed.

Run "TZ=UTC0 admin/update-copyright".