Add USES=7z support

[jbeich]

Summary

Common way to extract .7z files. Can take advantage of libarchive support. Maybe not very useful due to low number of consumers. See examples for usage.

Initial version is based on devel/fb-adb, so expect rough edges.

Test Plan

Build examples on 9.x and 10.x.

[jbeich]

devel/fb-adb: OVERRIDE_LINUX_BASE_PORT check can be easily killed now.

[jbeich]

Oops, fix USES=7z:partial regression: DISTFILES vs. _DISTFILES.

[bapt]

All targets should be done in a POST section

I have seen that other USES are not pushing target in a post section they must be fixed

otherwise looks good to me

[jbeich]

In D4190#103040, @bapt wrote:

All targets should be done in a POST section

Rationale? "Traditionally" isn't a valid one as rP394503 was designed to break it. For USES=7z the current order not only safeguards do-p7zip-extract from quirks in individual ports but also allows post-extract to fix up paths/etc after extraction of *.7z files, similar to *.tar.gz.

[mat]

@bapt, if by "post" section you mean the fact that the target is called do-* then it's irrelevant, it's run after the do-extract target, so it feels kinda ok to me.

[bapt]

yes you are right, my bad