bug#32189: 27.0.50; GCC 7 warning due to -Wformat-truncation=2

[Eli Zaretskii <eliz@gnu.org>]

> Cc: 32189@debbugs.gnu.org
> From: Ken Brown <kbrown@cornell.edu>
> Date: Thu, 19 Jul 2018 09:56:43 -0400
> 
> The attached patch suppresses the warning.
> 
> From e5efe43d9fa38ef10d88a4eaf88c5e7b8be9d5c8 Mon Sep 17 00:00:00 2001
> From: Ken Brown <kbrown@cornell.edu>
> Date: Thu, 19 Jul 2018 09:52:19 -0400
> Subject: [PATCH] Avoid warnings with GCC 7
> 
> * configure.ac (nw): Suppress the -Wformat-truncation=2 option
> due to too many false alarms with GCC 7.  (Bug#32189)
> ---
>  configure.ac | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/configure.ac b/configure.ac
> index b6918671e4..202c5621b1 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -954,6 +954,7 @@ AC_DEFUN
>  
>    nw="$nw -Wcast-align -Wcast-align=strict" # Emacs is tricky with pointers.
>    nw="$nw -Wduplicated-branches"    # Too many false alarms
> +  nw="$nw -Wformat-truncation=2"    # Too many false alarms
>    nw="$nw -Wformat-overflow=2"      # False alarms due to GCC bug 80776
>    nw="$nw -Wsystem-headers"         # Don't let system headers trigger warnings
>    nw="$nw -Woverlength-strings"     # Not a problem these days

Thanks, this LGTM, but I'd like to hear Paul's opinion about this
warning before we push (since this should probably go to the emacs-26
branch?).