Wrong GCC PR2020 annotated for "[committed, libgomp,amdgcn] Fix plugin-gcn.c bug"

[Jonathan Wakely]

On Thu, 23 Jan 2020 at 16:57, Andrew Stubbs wrote:
> Indeed, PR2019 has a number of unrelated commits referenced, and pr2018
> has one too. The years before that appear to have escaped the problem.

The 2019 ones are even more silly, as the unrelated commits were
correcting the PR number in some filenames!

I'll tag those bugzilla comments as "obsolete" so they're hidden by
default and don't confuse people.