y2038: utimes: Rework #ifdef guards for compat syscalls

After changing over to 64-bit time_t syscalls, many architectures will
want compat_sys_utimensat() but not respective handlers for utime(),
utimes() and futimesat(). This adds a new __ARCH_WANT_SYS_UTIME32 to
complement __ARCH_WANT_SYS_UTIME. For now, all 64-bit architectures that
support CONFIG_COMPAT set it, but future 64-bit architectures will not
(tile would not have needed it either, but got removed).

As older 32-bit architectures get converted to using CONFIG_64BIT_TIME,
they will have to use __ARCH_WANT_SYS_UTIME32 instead of
__ARCH_WANT_SYS_UTIME. Architectures using the generic syscall ABI don't
need either of them as they never had a utime syscall.

Since the compat_utimbuf structure is now required outside of
CONFIG_COMPAT, I'm moving it into compat_time.h.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
changed from last version:
- renamed __ARCH_WANT_COMPAT_SYS_UTIME to __ARCH_WANT_SYS_UTIME32

include/linux/time32.h

@@ -30,6 +30,11 @@ struct old_itimerspec32 {
 	struct old_timespec32 it_value;
 };
 
+struct old_utimbuf32 {
+	old_time32_t	actime;
+	old_time32_t	modtime;
+};
+
 extern int get_old_timespec32(struct timespec64 *, const void __user *);
 extern int put_old_timespec32(const struct timespec64 *, void __user *);
 extern int get_old_itimerspec32(struct itimerspec64 *its,