Avoid printf ("%s", NULL) in posix/bug-regex22.c.

Building posix/bug-regex22.c fails with GCC mainline because of
-Wformat-overflow= warnings for NULL arguments to %s formats.

This is *not* testing how glibc handles such format arguments; in the
context of the messages in question it makes no sense to pass NULL to
such a %s format (the code passes s, inside "if (s == NULL)").  So
this patch changes the code not to pass such a format argument at all
(which means the string passed is constant, so no need to use printf
at all - however, there are two separate tests here with different
length arguments passed to re_compile_pattern, so it *does* make sense
to make the strings used different so that in the event of failure
it's clear which one of the tests failed).

Tested with build-many-glibcs.py with GCC mainline for
aarch64-linux-gnu.

	* posix/bug-regex22.c (main): Use puts with distinct error
	messages for unexpected success of re_compile_pattern, not printf
	with NULL argument to %s.