Fix test-errno issues

Fix test-errno issues

This patch fixes multiple issues of test-errno.c (9a56f8718341):

  - Rename Linux test-errno.c to test-errno-linux.c to avoid build
    the same source for both tests.

  - Add a mlock check for 32 bits build running on 64 bits kernels.
    Althuough man pages states that mlock fails with EINVAL if final
    address overflows, kernels does not return it for aforementioned
    condition (it returns ENOMEM instead).  Although it seems to be
    a kernel issue for compat syscall handling, I think it is worth
    to still check syscall return and document the behavior.

  - Initialize option lenght for setsockopt check.

  - Change open test from EINVAL to EISDIR.

Checked on x86_64-linux-gnu and i686-linux-gnu (running on 64 bits
kernel).

	* posix/test-errno.c (do_test): Initialize setsockopt optlen.
	* sysdeps/unix/sysv/linux/test-errno.c: Move to ...
	* sysdeps/unix/sysv/linux/test-errno-linux.c: ... here.
	(test_wrp_rv): Fix format.
	(test_wrp_rv2): New macro.
	(do_test): Handle mlock return on 64 bits kernels with 32 bits
	binaries.