artifacts from builds

The autopkg tests have the ability to collect some information in artifacts, collected in a tarball. That kind of feature could be useful for builds as well, both for failing and succeeding builds.

 - A common artifact for failing builds is the config.log file,
   dumped to stdout by debhelper. Same for some cmake logs.

 - A reproducible compiler error (ICE) produces a /tmp/cc*.out
   containing the preprocessed source. This is used to trim down
   the source to a test case to be submitted upstream. It's
   extra work to setup a local build for the target arch, and
   re-running the build. The current approach is to dump this
   file to stdout and hoping that we don't run too much in
   parallel ending up in garbled output.

   OpenJDK has a similar feature which produces hs_err dump
   files.

 - Verbose test logs usually are not included in any package,
   but help diagnosing the problems without needing to do a
   local build. Many Gnome(?) builds have a verbose test log
   which has more information about the test runs. dejagnu
   based test suites produce *.sum and *.log files which contain
   all stdout/stderr output for a failing test case.

   Work around for dejagnu (e.g. GCC) is to have a separate
   binary package holding all the test results. Not ideal as
   it costs archive space, and the logs have the same lifetime
   as the binary packages.

 - For a test rebuild, I want to compare the config.h files
   generated by autoconf and look at the diff for each package
   (baseline build and test build).

The trigger what to include in these artifacts is sometime the package itself (test logs), sometimes another package used for the build (e.g. GCC), or even specific to the build (maybe only for the test rebuild).