gawk: disable persistent memory allocator due to licensing

gawk: disable persistent memory allocator due to licensing

In gawk-5.2, a feature that allows gawk to preserve memory between runs:
   https://www.gnu.org/software/gawk/manual/html_node/Persistent-Memory.html
was added. The files that implement this, support/pma.[ch], are licensed
under the AGPL3 which some entities perfer to avoid. Force people to knowingly
opt into using this feature and license using:
   PACKAGECONFIG:append:pn-gawk = " pma-if-64bit"
where pma is an abbreviation for persistent memory allocator and the
"-if-64bit" suffix is a indicator to users that the feature only works
for 64 bit targets. Also add AGPL to LICENSE and LICENSE:${PN}, when using pma.

Correct the license to be AGPL-3.0-or-later. There hasn't been a change in
the license terms, at least for main.c, haven't changed significantly in
the last 15 years:

License-Update: Reflects conditional AGPL use and more as described above.

Testing requires a non-root account and following the example in the link above:
  $ truncate -s <size> data.pma
  $ chmod 0600 data.pma
  $ GAWK_PERSIST_FILE=data.pma gawk 'BEGIN { print ++i }'
  1
  $ GAWK_PERSIST_FILE=data.pma gawk 'BEGIN { print ++i }'
  2
  $ GAWK_PERSIST_FILE=data.pma gawk 'BEGIN { print ++i }'
  3

This works on qemu[x86-|arm|riscv]64 but not on qemu[arm|x86] where the
--enable-pma is ignored because there is a requirement and build-time test
for 8 byte void pointers in m4/pma.m4:
  if test "$SKIP_PERSIST_MALLOC" = no && test $ac_cv_sizeof_void_p -eq 8

Finally, remove an old comment about GPLv2, GPLv3 versions of gawk
since this is no longer important as the GPLv2 version is not maintained.

Signed-off-by: Randy MacLeod <Randy.MacLeod@windriver.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>