posix: Add invalid flags test for p{write,read}v2

This patch add an extra test for passing invalid flags and check its
expected failure.  It shows an invalid LO_HI_LONG macro definition for
x86_64 with leads to passing invalid flags on some configurations.

The new tests fails on i686-linux-gnu and potentially on other 32 bits
architecture that uses the compat syscall definition due a kernel bug.
It is intended to be fixed upstream.

Checked on x86_64-linux-gnu

	* misc/tst-preadvwritev2-common.c: New file.
	* misc/tst-preadvwritev2.c (do_test): Add test for invalid flag.
	* misc/tst-preadvwritev64v2.c (do_test): Likewise.