master 5e5689a2a40: configure.ac: Fix FIONREAD check with gcc-14 on Solaris

[Stefan Kangas]

branch: master
commit 5e5689a2a40cd16d7593a0c7ddea5511adc3bf22
Author: Alan Coopersmith <alan.coopersmith@oracle.com>
Commit: Stefan Kangas <stefankangas@gmail.com>

    configure.ac: Fix FIONREAD check with gcc-14 on Solaris
    
    Before this fix, it would fail to build with gcc-14 with the error:
    conftest.c: In function 'main':
    conftest.c:265:11: error: implicit declaration of function 'ioctl'
     [-Wimplicit-function-declaration]
      265 | int foo = ioctl (0, FIONREAD, &foo);
          |           ^~~~~
    
    Solaris documents ioctl() as being defined in <unistd.h>.
    
    * configure.ac: Fix FIONREAD check with gcc-14 on Solaris.
    Ref:
    https://lists.gnu.org/r/emacs-devel/2024-10/msg00195.html
    
    Copyright-paperwork-exempt: yes
---
 configure.ac | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/configure.ac b/configure.ac
index 8a5ba7db3d1..947c2827b8e 100644
--- a/configure.ac
+++ b/configure.ac
@@ -7117,6 +7117,9 @@ AC_CACHE_CHECK([for usable FIONREAD], 
[emacs_cv_usable_FIONREAD],
                            #ifdef USG5_4
                            # include <sys/filio.h>
                            #endif
+                           #ifdef HAVE_UNISTD_H
+                           # include <unistd.h> /* defines ioctl() on Solaris 
*/
+                           #endif
                          ]],
                          [[int foo = ioctl (0, FIONREAD, &foo);]])],
         [emacs_cv_usable_FIONREAD=yes],