Show version of OpenSSL in ./configure output

Hi all,

5e4dacb9878c has reminded me that we don't show the version of OpenSSL
in the output of ./configure.  This would be useful to know when
looking at issues within the buildfarm, and I've wanted that a few
times.

How about the attached to use the openssl command, if available, to
display this information?  Libraries may be installed while the
command is not available, but in most cases I'd like to think that it
is around, and it is less complex than using something like
SSLeay_version() from libcrypto.

meson already shows this information, so no additions are required
there.  Also, LibreSSL uses `openssl`, right?

Thoughts or comments?
--
Michael