Make the following changes by hand, and run 'admin/merge-gnulib'.
* .gitignore: Add lib/malloc/*.gl.h.
* admin/merge-gnulib: Copy lib/af_alg.h and lib/save-cwd.h
directly from Gnulib, without worrying about Gnulib modules,
as these files are special cases.
(AVOIDED_MODULES): Remove malloc-posix.
* lib/malloc.c, lib/realloc.c, m4/malloc.m4, m4/realloc.m4:
* m4/year2038.m4: New files, copied from Gnulib.
* lib/malloca.c, lib/malloca.h:
* m4/close-stream.m4, m4/glibc21.m4, m4/malloca.m4:
Remove.  These are either no longer present in Gnulib, or are no
longer needed by modules that Emacs uses.
* oldXMenu/AddPane.c, oldXmenu/Addsel.c: Include XmenuInt.h first;
needed for new Gnulib.
* src/xmenu.c: Call emacs_abort, not abort.

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

This incorporates:
2020-02-08 lchmod: ensure declaration on HP-UX
2020-02-08 fchmodat: fix endless recursion on Cygwin
2020-02-08 Fix compilation errors in a testdir
2020-02-07 fchmodat: AT_SYMLINK_NOFOLLOW fix for non-symlinks
2020-02-04 Port _Noreturn to older Clang
2020-02-03 libc-config: port to Apple’s Clang variant
* lib/_Noreturn.h, lib/c++defs.h, lib/libc-config.h, lib/sys_stat.in.h:
* m4/gnulib-common.m4, m4/sys_stat_h.m4: Copy from Gnulib.
* lib/gnulib.mk.in: Regenerate.

Run "TZ=UTC0 admin/update-copyright $(git ls-files)".

This incorporates:
2019-12-06 nstrftime: better width support for %N, %z
2019-12-03 Avoid hassles caused by [[noreturn]] in C++
2019-12-02 Fix mistakes in --enable-threads=isoc fixes from 2019-12-01
* admin/merge-gnulib (AVOIDED_MODULES): Avoid pthread-h.
* lib/_Noreturn.h, lib/nstrftime.c, m4/gnulib-common.m4:
* m4/timer_time.m4:
Copy from Gnulib.
* lib/gnulib.mk.in: Regenerate.

This incorporates:
2019-04-07 Add copyright notices in several files
* build-aux/config.sub, doc/misc/texinfo.tex, lib/_Noreturn.h:
Copy from Gnulib.
* lib/gnulib.mk.in: Regenerate.

This incorporates:
2019-03-23 Support cross-compilation to musl libc
2019-03-23 noreturn: In C++ mode with clang, use _Noreturn as fallback
2019-03-22 _Noreturn: beware of C's _Noreturn in C++ pre C++11
2019-03-19 Help making signal handlers more reliable
2019-03-18 _Noreturn: clang and MSVC do support [[noreturn]] in C++11
2019-03-17 _Noreturn: GCC 4.7 does not support [[noreturn]] in C++11
2019-03-14 all: Update URLs to msdn.microsoft.com
* doc/misc/texinfo.tex, lib/_Noreturn.h, lib/gettimeofday.c:
* lib/mktime.c, lib/regcomp.c, lib/regexec.c, lib/stat-time.h:
* lib/utimens.c, m4/fdopendir.m4, m4/getgroups.m4:
* m4/gettimeofday.m4, m4/gnulib-common.m4, m4/putenv.m4, m4/utimes.m4:
Update from gnulib.

This incorporates:
2018-11-03 nstrftime: simplify test for mktime failure
2018-11-02 gnulib-common.m4: port _Noreturn to C++
2018-10-22 std-gnu11: Support Autoconf versions < 2.64
2018-10-22 Assume Autoconf >= 2.63
2018-10-16 Remove support for Ultrix
2018-10-16 getloadavg: Remove support for ConvexOS
2018-10-16 getloadavg: Remove support for Sony NEWS
2018-10-16 Remove support for Dynix/ptx
2018-10-16 fsusage: Remove support for AIX 3
2018-10-16 fsusage, stat-size, getloadavg: Remove support for AIX PS/2
2018-10-16 getloadavg: Remove support for HP-UX on m68k
2018-10-16 fsusage, mountlist: Remove support for DolphinOS
2018-10-16 getloadavg: Remove support for Alliant FX/2800
2018-10-16 getloadavg: Remove support for tek4300
2018-10-16 getloadavg: Remove support for Ardent
* build-aux/config.guess, build-aux/config.sub, lib/_Noreturn.h:
* lib/fsusage.c, lib/getgroups.c, lib/getloadavg.c:
* lib/nstrftime.c, lib/time.in.h, m4/errno_h.m4:
* m4/fsusage.m4, m4/getgroups.m4, m4/gnulib-common.m4, m4/longlong.m4:
* m4/std-gnu11.m4, m4/stdint.m4:
Copy from Gnulib.
* lib/gnulib.mk.in, m4/gnulib-comp.m4: Regenerate:

This incorporates:
2017-03-14 snippets: move unadjusted snippet sources to lib
2017-03-14 gnulib-tool: fix typo in comment output
2017-03-14 snippets: work around GNU Make 3.82 VPATH
2017-03-13 gnulib-tool: minor --gnu-make fixups
2017-03-12 gnulib-tool: new option --gnu-make
* .gitignore: Remove lib/arg-nonnull.h, lib/c++defs.h,
lib/warn-on-use.h.  Change exception from
build-aux/snippet/_Noreturn.h to lib/_Noreturn.h.
* admin/authors.el (authors-renamed-files-regexps):
* admin/notes/copyright, make-dist:
The snippet files moved from build-aux/snippet to lib.
* lib/_Noreturn.h: Rename from build-aux/snippet/_Noreturn.h.
* lib/arg-nonnull.h: Rename from build-aux/snippet/arg-nonnull.h.
* lib/c++defs.h: Rename from build-aux/snippet/c++defs.h.
* lib/gnulib.mk, m4/gnulib-comp.m4: Regenerate.
* lib/warn-on-use.h: Rename from build-aux/snippet/warn-on-use.h.