selftests: vDSO: quash clang omitted parameter warning in getrandom test

When building with clang, there's this warning:

vdso_test_getrandom.c:145:40: warning: omitting the parameter name in a function definition is a C23 extension [-Wc23-extensions]
  145 | static void *test_vdso_getrandom(void *)
      |                                        ^
vdso_test_getrandom.c:155:40: warning: omitting the parameter name in a function definition is a C23 extension [-Wc23-extensions]
  155 | static void *test_libc_getrandom(void *)
      |                                        ^
vdso_test_getrandom.c:165:43: warning: omitting the parameter name in a function definition is a C23 extension [-Wc23-extensions]
  165 | static void *test_syscall_getrandom(void *)

Add the named ctx parameter to quash it.
Reported-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

tools/testing/selftests/vDSO/vdso_test_getrandom.c

@@ -143,7 +143,7 @@ static ssize_t vgetrandom(void *buf, size_t len, unsigned long flags)
 
 enum { TRIALS = 25000000, THREADS = 256 };
 
-static void *test_vdso_getrandom(void *)
+static void *test_vdso_getrandom(void *ctx)
 {
 	for (size_t i = 0; i < TRIALS; ++i) {
 		unsigned int val;
@@ -153,7 +153,7 @@ static void *test_vdso_getrandom(void *)
 	return NULL;
 }
 
-static void *test_libc_getrandom(void *)
+static void *test_libc_getrandom(void *ctx)
 {
 	for (size_t i = 0; i < TRIALS; ++i) {
 		unsigned int val;
@@ -163,7 +163,7 @@ static void *test_libc_getrandom(void *)
 	return NULL;
 }
 
-static void *test_syscall_getrandom(void *)
+static void *test_syscall_getrandom(void *ctx)
 {
 	for (size_t i = 0; i < TRIALS; ++i) {
 		unsigned int val;