bug#68842: 29.2; implicit declaration of function 'XOpenDisplay'

[Eli Zaretskii <eliz@gnu.org>]

> From: Ulrich Müller <ulm@gentoo.org>
> Date: Wed, 31 Jan 2024 09:03:29 +0100
> 
> configure warns about an implicit function declaration for XOpenDisplay,
> which in turn triggers a QA warning in Gentoo's package manager.
> 
> The relevant snippet from configure.log is:
> 
> configure:14158: checking whether X on GNU/Linux needs -b to link
> configure:14175: x86_64-pc-linux-gnu-gcc -o conftest  -march=native -ggdb -O2 -pipe     -Wl,-O1 -Wl,--as-needed  conftest.c -lX11   >&5 
> conftest.c: In function 'main':
> conftest.c:125:1: warning: implicit declaration of function 'XOpenDisplay' [-Wimplicit-function-declaration]
>   125 | XOpenDisplay ("foo");
>       | ^~~~~~~~~~~~
> configure:14175: $? = 0
> configure:14223: result: no
> 
> Attached patch fixes the problem for me. Is it OK to merge it to the
> emacs-29 branch? (In master, the test in question was removed altogether
> by commit 6c1413d5ef0d1fea639b0d8c83a0c0065d99359b.)

Po Lu, any comments to the patch?

I don't mind installing this on emacs-29, if it's TRT, but the chances
for us to have another Emacs 29.x release are slim at best at this
point.  So I wonder whether you should bother.