Merge remote-tracking branch 'remotes/stefanha-gitlab/tags/tracing-pull-request'...

Merge remote-tracking branch 'remotes/stefanha-gitlab/tags/tracing-pull-request' into staging

Pull request

# gpg: Signature made Mon 12 Jul 2021 17:49:46 BST
# gpg:                using RSA key 8695A8BFD3F97CDAAC35775A9CA4ABB381AB73C8
# gpg: Good signature from "Stefan Hajnoczi <stefanha@redhat.com>" [full]
# gpg:                 aka "Stefan Hajnoczi <stefanha@gmail.com>" [full]
# Primary key fingerprint: 8695 A8BF D3F9 7CDA AC35  775A 9CA4 ABB3 81AB 73C8

* remotes/stefanha-gitlab/tags/tracing-pull-request:
  trace, lttng: require .pc files
  trace/simple: add st_init_group
  trace/simple: pass iter to st_write_event_mapping
  trace: add trace_event_iter_init_group
  trace: iter init tweaks
  qemu-trace-stap: changing SYSTEMTAP_TAPSET considered harmful.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>