gdbserver, aarch64: Zero out regs in aarch64_linux_set_debug_regs

[Joel Brobecker]

> Ok, cherry-picked and pushed. I also updated the wiki. Unfortunately
> there doesn't seem to be a PR for the issue.

In that case, we need to create one, which I just did for you.
The reason why we want a PR is that we want a short description
of the problem with a short link that also works in textual
format to the problem description. When we discussed this requirement
a while back, we settled on using bugzilla. A link to the mailing
list isn't as good, especially in a case like this where the email
thread got silent for a couple of months before resurecting. With
the PR, we can add information again anytime, and we know everything
will remain pieced together.

Long story short: You're good, now :).

Thanks!
-- 
Joel