bug#55294: Configure failure on Solaris 11.4

[Eli Zaretskii]

> From: Steve Downey <sdowney@gmail.com>
> Date: Fri, 6 May 2022 15:58:39 -0400
> 
> On solaris 11.4, the system libc has a definition of sqrt leading configure 
> to believe that linking libm is
> unnecessary.

Can you tell the details, please?  What is that definition of sqrt,
and what do you see in config.log when it is tested?

> Applying a patch locally to change
> AC_SEARCH_LIBS([sqrt], [m]) to 
> AC_SEARCH_LIBS([atan], [m])
> fixes the problem. 
> 
> atan was picked at random from the symbols that couldn't be found in building 
> temacs. 

This is fragile, because we could have the same problem with atan, in
the future or on some other platform, if not here and now.  I think we
should understand better why using sqrt leads to the wrong conclusion,
and modify configure to avoid that.

Thanks.