Debian/Ubuntu test rebuilds using GCC 7 (r243559)

[Matthias Klose <doko at ubuntu dot com>]

Here are the results of a first test rebuild of the Debian (amd64) and Ubuntu
(all architectures) archives.  The test was started with a GCC trunk around
20161202, and then build failures were retried later with r243559. I filed
around 10-15 issues for ICEs, the most of them already fixed on the trunk.

I'll be in vacation mode until January, so won't be able to do a further
analysis until next year, then hopefully with another rebuild using a recent
snapshot.

The build logs for the failing builds (but succeeding with GCC 6) can be found
at http://people.canonical.com/~doko/tmp/regressions-gcc7/

These are the regressions identified from these two test rebuilds:
http://qa.ubuntuwire.org/ftbfs/rebuilds/test-rebuild-20161202-zesty.html
http://qa.ubuntuwire.org/ftbfs/rebuilds/test-rebuild-20161202-gcc7-zesty.html

The build logs for the Debian amd64 test rebuild (done by Lucas Nussbaum) can be
found at

http://aws-logs.debian.net/2016/12/04.gcc7/00diff-results.txt
http://aws-logs.debian.net/2016/12/04.gcc7/00all-results.txt
http://aws-logs.debian.net/2016/12/04.gcc7/

Grep the first file for "OK Failed" to get the packages that succeeded
in unstable but failed with gcc7.

Scanning these build logs there is a number of failures unrelated to GCC 7, like

 - gnat not yet updated, GCC 6/7 mix is failing

 - packages recording GCC versions in public include files, and failing
   the build on mismatch (annoying ...)

If people want to have a look ...

 - the GCC 7 packages for Debian can be found in the experimental distribution

 - for Ubuntu use the PPA (zesty 17.04)
   https://launchpad.net/~ubuntu-toolchain-r/+archive/ubuntu/test/

Matthias