Merge patch series "nios2: Add architecture support for clone3"

Simon Schuster <schuster.simon@siemens-energy.com> says:

This series adds support for the clone3 system call to the nios2
architecture. This addresses the build-time warning "warning: clone3()
entry point is missing, please fix" introduced in 505d66d1abfb9
("clone3: drop __ARCH_WANT_SYS_CLONE3 macro"). The implementation passes
the relevant clone3 tests of kselftest when applied on top of
next-20250815:

	./run_kselftest.sh
	TAP version 13
	1..4
	# selftests: clone3: clone3
	ok 1 selftests: clone3: clone3
	# selftests: clone3: clone3_clear_sighand
	ok 2 selftests: clone3: clone3_clear_sighand
	# selftests: clone3: clone3_set_tid
	ok 3 selftests: clone3: clone3_set_tid
	# selftests: clone3: clone3_cap_checkpoint_restore
	ok 4 selftests: clone3: clone3_cap_checkpoint_restore

The series also includes a small patch to kernel/fork.c that ensures
that clone_flags are passed correctly on architectures where unsigned
long is insufficient to store the u64 clone_flags. It is marked as a fix
for stable backporting.

As requested, in v2, this series now further tries to correct this type
error throughout the whole code base. Thus, it now touches a larger
number of subsystems and all architectures.

Therefore, another test was performed for ARCH=x86_64 (as a
representative for 64-bit architectures). Here, the series builds cleanly
without warnings on defconfig with CONFIG_SECURITY_APPARMOR=y and
CONFIG_SECURITY_TOMOYO=y (to compile-check the LSM-related changes).
The build further successfully passes testing/selftests/clone3 (with the
patch from 20241105062948.1037011-1-zhouyuhang1010@163.com to prepare
clone3_cap_checkpoint_restore for compatibility with the newer libcap
version on my system).

* patches from https://lore.kernel.org/20250901-nios2-implement-clone3-v2-0-53fcf5577d57@siemens-energy.com:
  nios2: implement architecture-specific portion of sys_clone3
  arch: copy_thread: pass clone_flags as u64
  copy_process: pass clone_flags as u64 across calltree
  copy_sighand: Handle architectures where sizeof(unsigned long) < sizeof(u64)

Link: https://lore.kernel.org/20250901-nios2-implement-clone3-v2-0-53fcf5577d57@siemens-energy.com
Signed-off-by: Christian Brauner <brauner@kernel.org>