manylinux-policy: allow glibc component libanl

libanl was addedd to resolv in glibc 2.2.5 in 2001 to support async
dns queries.

It uses private GLIBC symbols, thus to ensure it works with higher
glibc runtime versions, it must be shared linked and should not be
vendored into the wheels. (similar to libdl / dlopen)

In 2021 with glibc 2.34 similar to many other split libraries, libanl
got folded into libc itself, and thus any applications that use async
dns queries no longer gain libanl NEEDED shared library dependency
with a stub remaining in place. (similar to libdl / libpthread etc).

Thus for policies between 2.2.5 and 2.33 there is a need to allow list
libanl, for example when vendoring modern builds of icu.

Longer term, it would be interested to support dropping libraries,
because policies built to manylinux 2.34 policy really should no
longer link with libanl / libdl / libpthread etc. As in all of those
libraries have now become no-op stubs.

Author: xnox