As per summary, and due to bug 706232. I realise that gcc:10, itself, is still in testing but 3.471 is three years old and it's a little frustrating to not be able to easily find bugs that have already been filed in the course of gcc:10 testing on an otherwise stable system (I was about to pull the trigger on a dup of the aforementioned bug).
I'll add a blocker on -fno-common as I've done for other such stabilisation bugs. It's imperfect but making sure fixes have propagated into stable matters before we can unleash GCC 10 anyway.
amd64 stable
x86 done
ppc done
ppc64 done
bug #764269 should be fixed now
@arm: ping!
not waiting with gcc-10 anymore
arm done all arches done