Cygwin: testsuite: fixes for compatibility with GCC 15

GCC 15 defaults to `-std=gnu23`, causing warnings in `testsuite` due to
pre-ANSI C function declarations. This patch updates the function
declarations to align with modern standards.

Signed-off-by: Thirumalai Nagalingam <[email protected]>

Author: thiru-mcw

winsup/testsuite/winsup.api/shmtest.c

@@ -75,9 +75,7 @@ key_t	shmkey;
 size_t	pgsize;
 
 int
-main(argc, argv)
-	int argc;
-	char *argv[];
+main(int argc, char **argv)
 {
 	struct sigaction sa;
 	struct shmid_ds s_ds;
@@ -178,17 +176,15 @@ main(argc, argv)
 }
 
 void
-sigsys_handler(signo)
-	int signo;
+sigsys_handler(int signo)
 {
 
 	tst_brkm (TBROK, cleanup,
 		"System V Shared Memory support is not present in the kernel");
 }
 
 void
-sigchld_handler(signo)
-	int signo;
+sigchld_handler(int signo)
 {
 	struct shmid_ds s_ds;
 	int cstatus;
@@ -235,9 +231,7 @@ cleanup()
 }
 
 void
-print_shmid_ds(sp, mode)
-	struct shmid_ds *sp;
-	mode_t mode;
+print_shmid_ds(struct shmid_ds *sp, mode_t mode)
 {
 	uid_t uid = geteuid();
 	gid_t gid = getegid();