linux-user: Implement fchmodat2 syscall

linux-user: Implement fchmodat2 syscall

The fchmodat2 syscall is new from Linux 6.6; it is like the
existing fchmodat syscall except that it takes a flags parameter.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/3019
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <20250710113123.1109461-1-peter.maydell@linaro.org>