Re-enable cpack FreeBSD generator

[adridg]

Summary

The generator causes segfaults because it doesn't call pkg_init()
(see https://gitlab.kitware.com/cmake/cmake/issues/18031).

• Do the initialization (to be submitted upstream) and related work.
• Introduce port OPTION to re-enable the generator (not by default, because it still fails stage-qa because of libarchive).

This still needs additional work because the case of the resulting
package is incorrect (e.g. produces file called Cmake-3.1.13.tgz,
but then tries copying cmake-3.1.13.tgz).

Test Plan

Create package with OPTION CPACK on, then (in the pou jail)
use cpack to create a CMake package, then install that somewhere else.

[mat]

devel/cmake/Makefile

59

PATCHDIR is for patches. This does not seem to be a patch but a regular file. In this case, you should be using FILESDIR.

(Yes, I know, PATCHDIR defaults to the same thing as FILESDIR.)

[adridg]

Match 3.11.4

[tcberner]

I think the CPACK option is a good idea -- so ship if after the change mat requested.