md5, sha1, sha256, sha512: support --with-openssl=auto-gpl-compat
* m4/gl-openssl.m4: Add a new "auto-gpl-compat" mode,
which will auto enable use of openssl, only for >= version 3,
which is newly licensed under the Apache Software License.
This will be used from coreutils for example by adding
gl_SET_CRYPTO_CHECK_DEFAULT([auto-gpl-compat]) to configure.ac.
Even though "auto-gpl-compat" is less aggressive than "auto",
we leave the default at "no" so projects can opt in to the
extra dependency.