* src/fns.c (Frequire): Doc fix to include the dynamic module
support.
* src/lread.c (Fload, Vload_suffixes): Doc fixes to include the
dynamic module support.
(Fload): Treat the module suffix the same as '*.el' and '*.elc'
wrt the MUST-SUFFIX argument.

* etc/NEWS: Expand documentation of dynamically loaded modules.

* configure.ac: Add '--with-modules' option.  Conditionally add
  dynlib.o and module.o to the list of objects.  Add any system
  specific flags to the linker flags to support dynamic libraries.
* m4/ax_gcc_var_attribute.m4: Add autoconf extension to test gcc
  attributes.
* src/Makefile.in: Conditionally add module objects and linker flags.
* src/alloc.c (garbage_collect_1): protect module local values from
  GC.
* src/lisp.h: Add 'module_init' and 'syms_of_module' prototypes.
* src/emacs_module.h: New header file included by modules.  Public
  module API.
* src/module.c: New module implementation file.

Co-authored-by: Philipp Stephani <phst@google.com>

* src/lisp.h: Add new Lisp_Misc_User_Ptr type.
(XUSER_PTR): New User_Ptr accessor.
* src/alloc.c (make_user_ptr): New function.
(mark_object, sweep_misc): Handle Lisp_Misc_User_Ptr.
* src/data.c (Ftype_of): Return 'user-ptr' for user pointer.
(Fuser-ptrp): New user pointer type predicate function.
(syms_of_data): New 'user-ptrp', 'user-ptr' symbol.  New 'user-ptrp'
subr.
* src/print.c (print_object): Add printer for User_Ptr type.

* lisp/net/soap-inspect.el (soap-inspect-xs-simple-type):
Fix misspelling in output.

* src/alloc.c (compact_font_cache_entry): Don't GC unmarked font
entities if some of the fonts it references are marked.  This
plugs a memory leak.  (Bug#21556)

* src/alloc.c (xnmalloc, xnrealloc, xpalloc, Fmake_string):
* src/buffer.c (record_overlay_string, overlay_strings):
* src/casefiddle.c (casify_object):
* src/ccl.c (Fccl_execute_on_string):
* src/character.c (char_width, c_string_width, lisp_string_width)
(count_size_as_multibyte, string_escape_byte8):
* src/coding.c (coding_alloc_by_realloc, produce_chars):
* src/data.c (arith_driver):
* src/dispnew.c (realloc_glyph_pool, init_display):
* src/editfns.c (styled_format):
* src/fns.c (Ffillarray):
* src/ftfont.c (ftfont_shape_by_flt):
* src/gnutls.c (gnutls_hex_string):
* src/gtkutil.c (get_utf8_string):
* src/image.c (x_to_xcolors, x_detect_edges, png_load_body):
* src/keymap.c (Fkey_description):
* src/lisp.h (SAFE_ALLOCA_LISP):
* src/term.c (encode_terminal_code):
* src/tparam.c (tparam1):
* src/xselect.c (x_property_data_to_lisp):
* src/xsmfns.c (smc_save_yourself_CB):
* src/xterm.c (x_term_init):
When checking for integer overflow, prefer INT_MULTIPLY_WRAPV to
more-complicated code involving division and/or
INT_MULTIPLY_OVERFLOW, and similarly for INT_ADD_WRAPV and
subtraction and/or INT_ADD_OVERFLOW.
* src/casefiddle.c (casify_object): Simplify multibyte size check.
* src/character.c: Remove some obsolete ‘#ifdef emacs’s.
* src/data.c (arith_driver): Also check for division overflow,
as that’s now possible given that the accumulator can now contain
any Emacs integer.
* src/lisp.h (lisp_word_count): Remove; no longer used.

(pointers_fit_in_lispobj_p, mmap_lisp_allowed_p): #ifdef DOUG_LEA_MALLOC.

Omit ‘#include "foo.h"’ unless the file needs foo.h (Bug#21707).
In a few cases, add ‘#include "foo.h"’ if the file needs foo.h
but does not include it directly.  As a general rule, a source
file should include foo.h if it needs the interfaces that foo.h
defines.
* src/alloc.c: Don’t include process.h.  Include dispextern.h,
systime.h.
* src/atimer.c: Don’t include blockinput.h.
* src/buffer.c: Include coding.h, systime.h.  Don’t include
keyboard.h, coding.h.
* src/callint.c: Don’t include commands.h, keymap.h.
* src/callproc.c: Don’t include character.h, ccl.h, composite.h,
systty.h, termhooks.h.
* src/casetab.c: Don’t include character.h.
* src/category.c: Don’t include charset.h, keymap.h.
* src/ccl.h: Don’t include character.h.
* src/character.c: Don’t include charset.h.
* src/charset.c: Don’t include disptab.h.
* src/chartab.c: Don’t include ccl.h.
* src/cm.c: Don’t include frame.h, termhooks.h.
* src/cmds.c: Don’t include window.h, dispextern.h.
* src/coding.c: Don’t include window.h, frame.h.
* src/composite.c: Include composite.h.  Don’t include window.h,
font.h.
* src/data.c: Don’t include syssignal.h, termhooks.h, font.h.
* src/dbusbind.c: Don’t include frame.h.
* src/decompress.c: Don’t include character.h.
* src/dired.c: Don’t include character.h, commands.h, charset.h.
* src/dispnew.c: Don’t include character.h, indent.h, intervals.h,
process.h, timespec.h.  Include systime.h.
* src/doc.c: Include coding.h.  Don’t include keyboard.h.
* src/editfns.c: Include composite.h.  Don’t include frame.h.
* src/emacs.c: Include fcntl.h, coding.h.  Don’t include
commands.h, systty.h..
* src/fileio.c: Don’t include intervals.h, dispextern.h.
Include composite.h.
* src/filelock.c: Don’t include character.h, systime.h.
* src/fns.c: Don’t include time.h, commands.h, keyboard.h,
keymap.h, frame.h, blockinput.h, xterm.h.  Include composite.h.
* src/font.c: Include termhooks.h.
* src/font.h: Don’t include ccl.h, frame.h.  Add forward decls of
struct composition_it, struct face, struct glyph_string.
* src/fontset.c: Don’t include buffer.h, ccl.h, keyboard.h,
intervals.h, window.h, termhooks.h.
* src/frame.c: Don’t include character.h, commands.h, font.h.
* src/frame.h: Don’t include dispextern.h.
* src/fringe.c: Don’t include character.h.
* src/ftcrfont.c: Don’t include dispextern.h, frame.h,
character.h, charset.h, fontset.h.
* src/ftfont.c: Don’t include frame.h, blockinput.h, coding.h,
fontset.h.
* src/ftxfont.c: Don’t include dispextern.h, character.h,
charset.h, fontset.h.
* src/gfilenotify.c: Don’t include frame.h, process.h.
* src/gtkutil.c: Include dispextern.h, frame.h, systime.h.
Don’t include syssignal.h, buffer.h, charset.h, font.h.
* src/gtkutil.h: Don’t include frame.h.
* src/image.c: Include fcntl.h and stdio.h instead of sysstdio.h.
Don’t include character.h.
* src/indent.c: Don’t include keyboard.h, termchar.h.
* src/inotify.c: Don’t include character.h, frame.h.
* src/insdel.c: Include composite.h.  Don’t include blockinput.h.
* src/intervals.c: Don’t include character.h, keyboard.h.
* src/intervals.h: Don’t include dispextern.h, composite.h.
* src/keyboard.c: Don’t include sysstdio.h, disptab.h, puresize.h.
Include coding.h.
* src/keyboard.h: Don’t incldue systime.h.
* src/keymap.c: Don’t include charset.h, frame.h.
* src/lread.c: Include dispextern.h and systime.h.
Don’t include frame.h.  Include systime.h.
* src/macros.c: Don’t include commands.h, character.h, buffer.h.
* src/menu.c: Include character.h, coding.h.  Don’t include
dispextern.h.
* src/menu.h: Don’t include systime.h.
* src/minibuf.c: Don’t include commands.h, dispextern.h, syntax.h,
intervals.h, termhooks.h.
* src/print.c: Include coding.h.  Don’t include keyboard.h,
window.h, dispextern.h, termchar.h, termhooks.h, font.h.
Add forward decl of struct terminal.
* src/process.c: Don’t include termhooks.h, commands.h,
dispextern.h, composite.h.
* src/region-cache.c: Don’t include character.h.
* src/scroll.c: Don’t include keyboard.h, window.h.
* src/search.c: Don’t include category.h, commands.h.
* src/sound.c: Don’t include dispextern.h.
* src/syntax.c: Don’t include command.h, keymap.h.
* src/sysdep.c: Don’t include window.h, dispextern.h.
* src/systime.h: Use ‘#ifdef emacs’, not ‘#ifdef EMACS_LISP_H’,
* src/term.c: Don’t include systty.h, intervals.h, xterm.h.
* src/terminal.c: Include character.h.
Don’t include charset.h, coding.h.
* src/textprop.c: Don’t include character.h.
* src/undo.c: Don’t include character.h, commands.h, window.h.
* src/unexsol.c: Don’t include character.h, charset.h.
* src/widget.c: Include widget.h.  Don’t include keyboard.h,
window.h, dispextern.h, blockinput.h, character.h, font.h.
* src/widgetprv.h: Don’t include widget.h.
* src/window.c: Don’t include character.h, menu.h, intervals.h.
* src/xdisp.c: Include composite.h, systime.h.  Don’t include
macros.h, process.h.
* src/xfaces.c: Don’t include charset.h, keyboard.h, termhooks.h,
intervals.h.
* src/xfns.c: Don’t include menu.h, character.h, intervals.h,
epaths.h, fontset.h, systime.h, atimer.h, termchar.h.
* src/xfont.c: Don’t include dispextern.h, fontset.h, ccl.h.
* src/xftfont.c: Don’t include dispextern.h, character.h, fontset.h.
* src/xgselect.c: Don’t include timespec.h, frame.h.
Include systime.h.
* src/xgselect.h: Don’t include time.h.
Use a forward decl to struct timespec instead.
* src/xmenu.c: Don’t include keymap.h, character.h, charset.h,
dispextern.h.  Include systime.h.
* src/xml.c: Don’t include character.h.
* src/xrdb.c [USE_MOTIF]: Don’t include keyboard.h.
* src/xselect.c: Don’t include dispextern.h, character.h,
buffer.h, process.h.
* src/xsmfns.c: Don’t include systime.h, sysselect.h.
* src/xterm.c: Don’t include syssignal.h, charset.h, disptab.h,
intervals.h process.h, keymap.h, xgselect.h.  Include composite.h.

* src/alloc.c (PURE_POINTER_P): Remove.
All uses replaced with PURE_P.
(XPNTR_OR_SYMBOL_OFFSET): New function.
(XPNTR): Move here from lisp.h.
Reimplement in terms of XPNTR_OR_SYMBOL_OFFSET.
(mark_maybe_object, valid_lisp_object_p, survives_gc_p):
Remove unnecessary cast.
(purecopy): Use XPNTR_OR_SYMBOL_OFFSET instead of XPNTR,
to avoid an unnecessary runtime test for symbols.
* src/lisp.h (lisp_h_XPNTR, XPNTR): Remove, moving XPNTR to alloc.c.
Only alloc.c needs XPNTR now.

* src/alloc.c (mark_object): Fix bug in checking code.
When GC_CHECK_MARKED_OBJECTS is defined, the bug caused
CHECK_ALLOCATED_AND_LIVE_SYMBOL to repeatedly do the
CHECK_ALLOCATED and CHECK_LIVE tests for the first symbol in each
bucket.  The bug did not affect behavior either in the normal case
where GC_CHECK_MARKED_OBJECTS is not defined, or where Emacs does
not have an internal error that a properly-written
CHECK_ALLOCATED_AND_LIVE_SYMBOL would detect.