configure: Disable building libcrypt by default

We mentioned eventual dropping of libcrypt in the 2.28 NEWS.  Actually
put that plan in motion by first disabling building libcrypt by default.
note in NEWS that the library will be dropped completely in a future
release.

Also add a couple of builds into build-many-glibcs.py.

Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
Reviewed-by: Andreas K. Hüttel <dilfridge@gentoo.org>