sparc: Add architecture support for clone3

sparc: Add architecture support for clone3

Add support for the clone3 system call to the SPARC architectures.

The implementation follows the pattern of the original clone syscall.
However, instead of explicitly calling kernel_clone, the clone3
handler calls the generic sys_clone3 handler in kernel/fork.
In case no stack is provided, the parents stack is reused.

The return value convention for clone3 follows the regular kernel return
value convention (in contrast to the original clone/fork on SPARC).

Closes: https://github.com/sparclinux/issues/issues/10
Signed-off-by: Ludwig Rydberg <ludwig.rydberg@gaisler.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Andreas Larsson <andreas@gaisler.com>
Tested-by: Andreas Larsson <andreas@gaisler.com>
Tested-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Link: https://lore.kernel.org/r/20260119144753.27945-3-ludwig.rydberg@gaisler.com
Signed-off-by: Andreas Larsson <andreas@gaisler.com>