New branch zack/ac-prog-lex-rewrite, please test

[Zack Weinberg]

Yesterday I got all the way through a major rewrite of AC_PROG_LEX
before realizing it didn't actually solve any of the problems with
"Software Generation Utilities (SGU) Solaris-ELF (4.0)" lex (as shipped
by OmniOS and I presume also OpenIndiana).  I think the changes I made
might still be worth doing, but they're quite invasive and in particular
may change the behavior of AC_PROG_LEX's compatibility mode undesirably.
Therefore, I do not plan to include them in Autoconf 2.72.

Instead, I pushed all the changes to a new branch in savannah:

https://git.savannah.gnu.org/cgit/autoconf.git/log/?h=zack/ac-prog-lex-rewrite

I'd like to land these changes early in the 2.73 cycle, so I invite
testing now.  Testing of the compat mode, and testing of interactions
with Automake, are particularly helpful.  Testing with Sun lex is *not*
helpful at this time; the problems discussed in the thread starting at
https://lists.gnu.org/archive/html/bug-autoconf/2023-12/msg00005.html
have not been fixed.  However, testing of other non-Flex implementations
of lex *is* helpful. I may make further changes on this branch; see the
TODO list in the commit message.

This message is going out to a bunch of people who reported difficulties
with AC_PROG_LEX in the past, as well as to autoconf@gnu.org.  If you
have not previously tried to test a git checkout of Autoconf, see
'README-hacking' (*not* 'HACKING') at top level of the source tree
for instructions.

zw