sched: Add __ASSEMBLY__ guards around struct clone_args

sched: Add __ASSEMBLY__ guards around struct clone_args

The addition of struct clone_args to uapi/linux/sched.h is not protected
by __ASSEMBLY__ guards, causing a failure to build from source for glibc
on RISC-V. Add the guards to fix this.

Fixes: 7f192e3cd316 ("fork: add clone3")
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Cc: <stable@vger.kernel.org>
Acked-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20190917071853.12385-1-seth.forshee@canonical.com
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>