Integrate GNU poke in GDB

Integrate GNU poke in GDB

This patch integrates GNU poke (http://jemarch.net/poke) in GDB by
mean of libpoke.  It allows the GDB user to execute Poke code from
within the debugger with access to the target memory, types and
values.

How this stuff works:

- GDB links with libpoke.so and uses the interface in libpoke.h.
  This is also how the GNU poke application (the command-line
  editor) is implemented.

- There are three commands:

  poke STR
  poke-add-type EXPR
  poke-add-types REGEXP
  poke-dump-types

  All three commands make sure to start the poke incremental
  compiler if it isn't running already.

- Access to the target's memory is provided by GDB by installing
  a Foreign IO device in the incremental compiler.  This is
  `iod_if' in poke.c.

- Access to the terminal is provided by GDB by providing a
  pk_term_if implementation to the incremental compiler.  This is
  `poke_term_if' in poke.c.

- Access to GDB values is provided by GDB by installing an alien
  token handler in the incremental compiler.  This is
  `poke_alien_token_handler' in poke.c.

gdb/ChangeLog:

2021-05-10  Jose E. Marchesi  <jose.marchesi@oracle.com>

	* configure.ac: Support --enable-poke.
	* configure: Regenerate.
	* Makefile.in (POKE_OBS): Define based on @POKE_OBS@.
	(DEPFILES): Add POKE_OBS.
	* poke.c: New file.

gdb/doc/ChangeLog:

2021-05-10  Jose E. Marchesi  <jose.marchesi@oracle.com>

	* Makefile.in (GDB_DOC_FILES): Add poke.texi.
	* poke.texi: New file.
	* gdb.texinfo (Data): Add meny entry for Poke and @include poke.texi.