Support SSL_R_VERSION_TOO_LOW when using LibreSSL

Support SSL_R_VERSION_TOO_LOW when using LibreSSL

The SSL_R_VERSION_TOO_LOW error reason is supported in LibreSSL since
LibreSSL 3.6.3, shipped in OpenBSD 7.2.  SSL_R_VERSION_TOO_HIGH is on
the other hand not supported in any version of LibreSSL.  Previously
we only checked for SSL_R_VERSION_TOO_HIGH and then applied both under
that guard since OpenSSL has only ever supported both at the same time.
This breaks the check into one per reason to allow SSL_R_VERSION_TOO_LOW
to work when using LibreSSL.

Reviewed-by: Peter Eisentraut <peter@eisentraut.org>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/eac70d46-e61c-4d71-a1e1-78e2bfa19485@eisentraut.org