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

[Julien Fischer]

On Mon, 7 Jun 2021, Peter Wang wrote:

> 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?

The correct fix (as per the comment I added to configure.ac) is to use
AC_PROG_LEX([noyywrap]), but that's only supported by 2.70+.

>> 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?

Yes, it works.  Doing that will mean that the configure output will use
a different quoting style from configure --help (which is fine by me).

Julien.