flex version

[Joseph S. Myers]

The current documentation of prerequisite software versions says:

   Flex version 2.5.4 (or later)
          Necessary when modifying *.l files.

          Necessary to build GCC during development because the generated
          output files are not included in the CVS repository. They are
          included in releases.

We may need to specify flex 2.5.4/2.5.4a (exactly) for use in the building
of release tarballs, as apparently <http://bugs.debian.org/196800> more
recent versions have abandoned portability of the generated files to any
host system without <stdint.h>, e.g. NetBSD 1.5 and Solaris 9.

-- 
Joseph S. Myers
jsm28@cam.ac.uk