Add Option to use Distfiles Mirror as a Fallback

[Calandracas606]

This adds an optional configuration to add a fallback distfiles mirror

The idea is that normally, distfiles should be fetched from the urls in the template. However, occasionally the urls have rotted, or are simply own temporarily, in which case the fetch will fail. A workaround to this has been to use the XBPS_DISTFILES_MIRROR option, however the downside to this is that it costs bandwidth, and 99% of the time isn't needed.

This adds the $XBPS_DISTFILES_FALLBACK option, which can be set to an addiontional list of mirrors which will be attempted after both $XBPS_DISTFILES_MIRROR, and the urls in the template have failed to fetch the distfiles

Testing the changes

• I tested the changes in this PR: YES

[Calandracas606]

this PR was tested using the fbreader package

url in the template is broken:

• http://www.fbreader.org/files/desktop/fbreader-sources-0.99.4.tgz

but the distfiles are available at https://sources.voidlinux.org/ :

• https://sources.voidlinux.org/fbreader-0.99.4/fbreader-sources-0.99.4.tgz

[github-actions[bot]]

Pull Requests become stale 90 days after last activity and are closed 14 days after that. If this pull request is still relevant bump it or assign it.

[Calandracas606]

bump

[github-actions[bot]]

Pull Requests become stale 90 days after last activity and are closed 14 days after that. If this pull request is still relevant bump it or assign it.