Convert devel/protobuf-c to USE_GITHUB

[truckman]

Summary

Convert to USE_GITHUB. This requires USES=autoreconf, but eliminates
the need for USES=pathfix as well as a patch.

Test Plan

Compare packages before and after this change.

Build on multiple versions of FreeBSD.

[mat]

You could keep the mirror on MASTER_SITE_LOCAL, setting MASTER_SITES= GH LOCAL/truckman/farsight. You can commit either version, as you prefer :-)

[truckman]

In D2234#3, @mat wrote:

You could keep the mirror on MASTER_SITE_LOCAL, setting MASTER_SITES= GH LOCAL/truckman/farsight. You can commit either version, as you prefer :-)

I think I'll go with the simple version so I don't have to keep my local mirror up to date.

[truckman]

Closed by commit rP383422 (authored by @truckman).