scripts: add autostuff stuff

scripts: add autostuff stuff

To be noted:

- the lex/yacc/gperf generated files include one another, so it is
  not possible to use proper automake constructs to generate the
  lexer

- it is possible to tell bison and flex to change the prefix of the
  generated symbols, different from the default 'yy'; but if one
  does so, then the names of the generated files also include this
  prefix instead of the default (here, we use 'zconf' instead of 'yy'

- autoconf has a /built-in/ check for lex, but has no way to know
  that the output files is differently named

Because of all these mis-features, the autostuff files contain some
dubious constructs, as a palliative.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>