-Add a SASL/LDAP option for mysql57-client
-Fix plugin.cmake for "FreeBSD != Linux" case
For new plugin, MySQL build assumes everything is MacOS or Windows or Linux.
This breaks upgrades when you have SASL/LDAP client-library installed.
Because it "Decides" that you "Want" SASL/LDAP support and tries to build it.
PR: 220865
Submitted by: mmokhi
Reported by: Vladimir Omelchuk <admin@vladiom.com.ua>
Reviewed by: mat, feld (mentors)
Approved by: feld (mentor)
MFH: 2017Q3
Differential Revision: https://reviews.freebsd.org/D11667