All the kernel routines were seen to be significantly slower
with these relatively recent components on an i3-2310M system:
kernel-4.10.6-200.fc25.x86_64
openssl-1.0.2m-1.fc25.x86_64
sha1 was nearly twice as slow in the kernel for example,
compared to the libcrypto routines.
Further considerations why this should not be the default, at:
https://lists.gnu.org/r/coreutils/2018-06/msg00034.html
* m4/af_alg.m4: Require --with-linux-crypto to enable.
* m4/gl-openssl.m4: Tweak accordingly.