Switch default man directory to /usr/local/share/man on FreeBSD

Summary:
In 2017, a proposal is made to simplify directory management,
and use /usr/local/share/man to adapt /usr/share/man instead
of the legacy /usr/local/man directory.

That proposal gained traction recently, as WindRiver fresh installation
doesn't have any man page installed to /usr/local/man. In fact, the folder
doesn't even exists.

Reference: https://lists.freebsd.org/pipermail/freebsd-ports/2017-March/107584.html

Test Plan:
Tested to deploy salt-wrapper unit on WindRiver
fresh installation under FreeBSD 14.1.

Reviewers: DorianWinty

Reviewed By: DorianWinty

Differential Revision: https://devcentral.nasqueron.org/D3482