Discriminate between configure failures and post-configure failures

[karkhaz]

We do not currently categorise build failures as happening during or after configure. We should be able to use libred to do this; it should hopefully be easy to find the invocation of configure, and its corresponding exit code.

This is so that we can give an exact number for how many things have broken configure scripts. It will also be interesting to identify what kind of configure script it is: Autoconf, hand-written, etc.