Merge remote-tracking branch 'remotes/stsquad/tags/pull-testing-next-251019-3' into...

Merge remote-tracking branch 'remotes/stsquad/tags/pull-testing-next-251019-3' into staging

Testing updates (split from mega PR)

  - various Travis dependency updates
  - enable tcg debug for check-tcg
  - additional Xcode build for Cirrus
  - dependency tweak for gitlab

# gpg: Signature made Fri 25 Oct 2019 20:35:56 BST
# gpg:                using RSA key 6685AE99E75167BCAFC8DF35FBD0DB095A9E2A44
# gpg: Good signature from "Alex Bennée (Master Work Key) <alex.bennee@linaro.org>" [full]
# Primary key fingerprint: 6685 AE99 E751 67BC AFC8  DF35 FBD0 DB09 5A9E 2A44

* remotes/stsquad/tags/pull-testing-next-251019-3:
  tests/docker: update Travis image to a more current version
  tests/docker: set HOST_ARCH if we don't have ARCH
  travis.yml: --enable-debug-tcg to check-tcg
  gitlab-ci.yml: Use libvdeplug-dev to compile-test the VDE network backend
  travis.yml: cache the clang sanitizer build
  tests/vm/netbsd: Disable IPv6
  tests/vm: Let subclasses disable IPv6
  cirrus.yml: add latest Xcode build target
  travis.yml: bump Xcode 10 to latest dot release
  travis.yml: Test the release tarball
  travis.yml: Fix the ccache lines
  travis.yml: Use newer version of libgnutls and libpng
  travis.yml: Use libsdl2 instead of libsdl1.2, and install libsdl2-image
  travis.yml: Add libvdeplug-dev to compile-test net/vde.c
  travis.yml: reduce scope of the --enable-debug build

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