selftests/nolibc: syscall_args: use generic __NR_statx

Compiling nolibc-test.c for rv32 got such error:

    tools/testing/selftests/nolibc/nolibc-test.c:599:57: error: ‘__NR_fstat’ undeclared (first use in this function)
      599 |   CASE_TEST(syscall_args);      EXPECT_SYSER(1, syscall(__NR_fstat, 0, NULL), -1, EFAULT); break;

The generic include/uapi/asm-generic/unistd.h used by rv32 doesn't
support __NR_fstat, use the more generic __NR_statx instead:

    Running test 'syscall'
    69 syscall_noargs = 1                                            [OK]
    70 syscall_args = -1 EFAULT                                      [OK]

__NR_statx has been added from v4.10:

    commit a528d35e ("statx: Add a system call to make enhanced file info available")

It has been supported by all of the platforms since at least from v4.20.

Suggested-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/linux-riscv/ee8b1f02-ded1-488b-a3a5-68774f0349b5@app.fastmail.com/


Signed-off-by: Zhangjin Wu <falcon@tinylab.org>
Reviewed-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>