[m-rev.] diff: do not warn about obsolete autoconf macros

[Peter Wang]

On Mon, 07 Jun 2021 15:19:55 +1000 Julien Fischer <jfischer at opturion.com> wrote:
> 
> From autoconf 2.70 onwards, obsolescence warnings are enabled by default.
> Recently I have fixed all the warnings we were getting, except for:
> 
> 1. With autoconf 2.70 we get a warning about our use of AC_PROG_LEX;
> this cannot be avoided while preserving support for autoconf 2.69

Can we use AC_PATH_PROG to search for flex instead?

> 
> 2. Warnings about escaping of quotes and double quotes, like:
> 
>      warning: back quotes and double quotes must not be escaped in:
>      $as_me:${as_lineno-$LINENO}: WARNING: cannot find a working \`mkfifo' or \`mknod'
> 
> I haven't (yet) found a way to avoid this warning and get a configure
> script that works :-(  Suggestions welcome.

Does 'single quotes' work?

Peter