vdso: Add struct __kernel_old_timeval forward declaration to gettime.h

The prototype of __vdso_gettimeofday() uses this struct. However
gettime.h's own includes do not provide a definition for it.

Add a forward declaration, similar to other used structs.

Fixes: 42874e4eb35b ("arch: vdso: consolidate gettime prototypes")
Signed-off-by: Thomas Weißschuh <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>
Link: https://lore.kernel.org/all/[e-mail]

include/vdso/gettime.h

···
 #include <linux/types.h>
 
 struct __kernel_timespec;
+struct __kernel_old_timeval;
 struct timezone;
 
 #if !defined(CONFIG_64BIT) || defined(BUILD_VDSO32_64)