[gcc r16-7926] Fortran: Caf_shmem - Fix compile issue on cygwin [PR124371]

[Andre Vehreschild]

https://gcc.gnu.org/g:9282a60d5ba0fe71756c2541d3f6b92b27d7b4b6

commit r16-7926-g9282a60d5ba0fe71756c2541d3f6b92b27d7b4b6
Author: Andre Vehreschild <vehre@gcc.gnu.org>
Date:   Fri Mar 6 10:38:47 2026 +0100

    Fortran: Caf_shmem - Fix compile issue on cygwin [PR124371]
    
    libgfortran/ChangeLog:
    
            PR libfortran/124371
            * caf/shmem/supervisor.c (startWorker): Use defined(HAVE_FORK)
            instead of !defined(WIN32) for preprocessor conditional.

Diff:
---
 libgfortran/caf/shmem/supervisor.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libgfortran/caf/shmem/supervisor.c b/libgfortran/caf/shmem/supervisor.c
index cdb318d5910e..6068533c7469 100644
--- a/libgfortran/caf/shmem/supervisor.c
+++ b/libgfortran/caf/shmem/supervisor.c
@@ -300,7 +300,7 @@ startWorker (image *im __attribute__ ((unused)),
   return true;
 }
 
-#ifndef WIN32
+#ifdef HAVE_FORK
 static void
 kill_all_images (supervisor *m)
 {