Emacs 28.1 built with x32 ABI outperforms x86-64

[Sven Hartrumpf]

Dear Emacs users.

With the new release of Emacs, I tried to build it with the x32 ABI.
I succeeded for the first time (gave up with earlier OS versions) and
it even worked without any problems (Ubuntu 21.10, gcc 11.2).

A small benchmark ("make check" followed by reproducing all .elc files)
outperforms the equivalent x86-64 version by 8 %.
Memory usage is almost half of x86-64, when opening files of several 100 MB.

Limitations:
- x32 has a hard memory limit of 4 GB.
- To avoid building too many dependencies for x32, I used the following
  configure line: ./configure --with-sound=no --without-dbus --without-x
- I had to build 12 x32 versions:
  gnutls autoconf ncurses nettle libidn2 libtasn1 p11-kit libgmp libtool libffi 
guile-2.2 gc
  (Ask me if you need more details.)

Greetings
Sven