GCC 10 now the default gcc in groovy

[Matthias Klose]

Debian started the move to GCC 10 earlier this week, and we are seeing now build
failures in groovy-proposed, mostly for symbols files only adjusted for GCC 10,
breaking builds with GCC 9.  That's why I'm doing the gcc-defaults change now in
Ubuntu as well, instead of early August as planned on the groovy release
schedule.  According to the release schedule there is no other major work
planned during that time (the binutils update is already done) [1].

We don't have have a recent test rebuild for groovy; I'll start one when we are
able to do one.  Until then, there is (outdated) information about the issues
introduced by GCC 10.  See the logs for an early test rebuild [2] for focal, and
the bugs filed for Debian [3].

Matthias

[1] https://discourse.ubuntu.com/t/groovy-gorilla-release-schedule/15531
[2]
https://people.canonical.com/~doko/ftbfs-report/test-rebuild-20200327-focal-gcc10-focal.html
[3]
http://bugs.debian.org/cgi-bin/pkgreport.cgi?tag=ftbfs-gcc-10;users=debian-gcc@lists.debian.org