winpthreads: testcases: Silence a Clang 23 warning about unused-but-set-global

This fixes the following warning (that is treated as an error
in CI):

    ../../tests/pthread_barrier/barrier4.c:50:12: warning: variable 'otherThreadCount' set but not used [-Wunused-but-set-global]
       50 | static int otherThreadCount = 0;
          |            ^

Signed-off-by: Martin Storsjö <martin@martin.st>

mingw-w64-libraries/winpthreads/tests/pthread_barrier/barrier4.c

diff --git a/mingw-w64-libraries/winpthreads/tests/pthread_barrier/barrier4.c b/mingw-w64-libraries/winpthreads/tests/pthread_barrier/barrier4.c
index 042992d..9098941 100644
--- a/mingw-w64-libraries/winpthreads/tests/pthread_barrier/barrier4.c
+++ b/mingw-w64-libraries/winpthreads/tests/pthread_barrier/barrier4.c
@@ -104,6 +104,8 @@
       assert(pthread_barrier_destroy(&barrier) == 0);
     }
 
+  (void) otherThreadCount;
+
   assert(pthread_mutex_destroy(&mx) == 0);
 
   return 0;