Retire the old GCC external toolchain ports.

[jhb]

Summary

These have been supplanted by the devel/freebsd-gcc6 port which uses
separate flavors for each target architecture and bundles the
CROSS_TOOLCHAIN makefile.

[jhb]

Li-wen, do we still have any CI jobs using the old ports?

[lwhsu]

In D30765#691683, @jhb wrote:

Li-wen, do we still have any CI jobs using the old ports?

No, we have all migrated to newer devel/freebsd-gcc*.

[jrm]

For the MOVED entries, the . should be removed. See Tools/scripts/MOVEDlint.awk.

Nitpicky: I think it makes more sense to describe the flavor as singular. The single port on the line has been replaced by a single flavor, so something like Replaced by a flavor.

[jhb]

• Update MOVED entries per jrm@'s feedback.