Merge remote-tracking branch 'remotes/stsquad/tags/pull-rc3-testing-and-tcg-201119...

A few test and doc fixes:

  - tweak DEBUG behaviour for vm-test-build
  - rename and update plug docs for versioning
  - slim down MAIN_SOFTMMU_TARGETS

# gpg: Signature made Wed 20 Nov 2019 10:56:23 GMT
# 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-rc3-testing-and-tcg-201119-1:
  tests/tcg: modify multiarch tests to work with clang
  .travis.yml: drop 32 bit systems from MAIN_SOFTMMU_TARGETS
  docs/devel: update tcg-plugins.rst with API versioning details
  docs/devel: rename plugins.rst to tcg-plugins.rst
  tests/vm: make --interactive (and therefore DEBUG=1) unconditional

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