ylwrap: fix C++ support for Bison

ylwrap: fix C++ support for Bison

Fixes automake bug#7648.

The current logic of ylwrap is to call yacc in a sub directory, and
pull out of it all the files that were requested on its command line.
Reverse this approach: export *all* the files created in the
subdirectory, but rename them according to what the command says.
This way, extra files, such as position.hh, location.hh and stack.hh
for C++ parsers, but also parser.xml or parser.dot if XML or Dot
output is enabled, will be preserved.

* lib/ylwrap (pairlist): Remove.
(main loop): Don't loop over pairlist, but over the files in the
temporary directory.
* t/list-of-tests.mk (XFAIL_TESTS): Fixes t/yacc-bison-skeleton-cxx.sh.
* THANKS (James Bostock): Add, he reported bug#7648.

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>