Re: master a86c25c91f3 11/13: Prefer -I to -isystem

[Eli Zaretskii <eliz@gnu.org>]

> branch: master
> commit a86c25c91f39a25a93d18c9267e024822c1bc43e
> Author: Paul Eggert <eggert@cs.ucla.edu>
> 
>     Prefer -I to -isystem
>     
>     * configure.ac: Simplify configuration by using -I instead of
>     -isystem, as -isystem is no longer helpful for suppressing
>     diagnostics (and likely has not been helpful for years).
>     Do not suppress -Wsystem-headers, as Gnulib no longer enables it.

Paul,

Contrary to your "famous last words" above, this change caused the
build issue a useless diagnostic in image.c, in a 32-bit build:

  d:/usr/include/glib-2.0/gobject/gparam.h:157:35: warning: result of '1 << 31' requires 33 bits to represent, but 'int' only has 32 bits [-Wshift-overflow=]
    157 |   G_PARAM_DEPRECATED          = 1 << 31
	|                                   ^~

While arguably a bug in Glib, the diagnostic is an annoyance, so I'd
like to avoid it.  I've verified that -Wno-system-headers doesn't
remove it.  -Wno-shift-overflow does, but I don't think suppressing
that globally is a good idea.