gawk: update to 5.3.0.

Changes from 5.2.x to 5.3.0
---------------------------

1. Infrastructure changes: Removed the use of libsigsegv. The
  value-add was never very much and it caused problems in some
  environments.

2. In keeping with new features in BWK awk, gawk now has built-in
  CSV file parsing. The behavior is intended to be identical to
  that of the "One True AWK" when --csv is applied. See the
  manual for details.

3. Also in keeping with BWK awk, gawk now supports a new \u escape
  sequence. This should be followed by 1-8 hexadecimal digits. The
  given code point is converted to its corresponding multibyte encoding
  for storage inside gawk. See the manual.

4. If PROCINFO["BUFFERPIPE"] exists, then pipe output is buffered.
  You can also use PROCINFO["command", "BUFFERPIPE"]. See the manual
  for details.

5. Because of the additional `do_csv' variable in the API, which breaks
  binary compatibility, the API major version was updated to 4 and
  the minor version was reset to zero.  The API remains source code
  compatible; that is, existing extensions should only require recompilation.

6. The manual now requires Texinfo 7.1 and its texinfo.tex for formatting.
  As a result, we no longer need to pre-process it, removing the need
  for gawktexi.in and leaving just gawk.texi.

7. And of course, there have been several minor code cleanups and bug fixes.
  See the ChangeLog for details.

Changes from 5.2.2 to 5.2.x
---------------------------

1. The readdir extension has been updated with additonal code and
  features, see the manual or its man page. As a result, the
  readdir_test.c extension has been removed.

2. We have a new translation: Ukranian.

3. Several subtle issues related to null regexp matches around
  multibyte characters have been fixed.

(wiz)