selftests/nolibc: disable coredump via setrlimit

qemu-user does has its own implementation of coredumping.
That implementation does not respect the call to
prctl(PR_SET_DUMPABLE, 0) in run_protection().
This leads to a coredump for every test run under qemu-user.

Use also setrlimit() to inhibit coredump creation which is respected by
qemu-user.

Link: https://lore.kernel.org/qemu-devel/20231115-qemu-user-dumpable-v1-2-edbe7f0fbb02@t-8ch.de/Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Link: https://lore.kernel.org/lkml/20231123-nolibc-rlimit-v1-3-a428b131de2a@weissschuh.net/Acked-by: Willy Tarreau <w@1wt.eu>

tools/testing/selftests/nolibc/nolibc-test.c

@@ -1166,6 +1166,7 @@ static int run_protection(int min __attribute__((unused)),
 {
 	pid_t pid;
 	int llen = 0, status;
+	struct rlimit rlimit = { 0, 0 };
 
 	llen += printf("0 -fstackprotector ");
 
@@ -1197,6 +1198,7 @@ static int run_protection(int min __attribute__((unused)),
 		close(STDERR_FILENO);
 
 		prctl(PR_SET_DUMPABLE, 0, 0, 0, 0);
+		setrlimit(RLIMIT_CORE, &rlimit);
 		smash_stack();
 		return 1;