selftests/futex: Convert 32-bit timespec to 64-bit version for 32-bit compatibility mode

sys_futex_wait() expects a struct __kernel_timespec pointer for the
timeout, but the provided struct timespec pointer is of type struct
old_timespec32 when compiled for 32-bit architectures, unless they use
64-bit timespecs already.

Make it work for all variants by converting the provided timespec value
into a local struct __kernel_timespec and provide a pointer to it to the
syscall. This is a pointless operation for 64-bit, but this is not a
hotpath operation, so keep it simple.

This fix is based off [1]

Originally-by: Wei Gao <wegao@suse.com>
Signed-off-by: Terry Tritton <terry.tritton@linaro.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250704190234.14230-1-terry.tritton@linaro.org
Link: https://lore.kernel.org/all/20231203235117.29677-1-wegao@suse.com/ [1]

Author: Terry Tritton

tools/testing/selftests/futex/include/futex2test.h

@@ -4,6 +4,7 @@
  *
  * Copyright 2021 Collabora Ltd.
  */
+#include <linux/time_types.h>
 #include <stdint.h>
 
 #define u64_to_ptr(x) ((void *)(uintptr_t)(x))
@@ -65,7 +66,12 @@ struct futex32_numa {
 static inline int futex_waitv(volatile struct futex_waitv *waiters, unsigned long nr_waiters,
 			      unsigned long flags, struct timespec *timo, clockid_t clockid)
 {
-	return syscall(__NR_futex_waitv, waiters, nr_waiters, flags, timo, clockid);
+		struct __kernel_timespec ts = {
+			.tv_sec = timo->tv_sec,
+			.tv_nsec = timo->tv_nsec,
+		};
+
+		return syscall(__NR_futex_waitv, waiters, nr_waiters, flags, &ts, clockid);
 }
 
 /*