Merge remote-tracking branch 'remotes/stsquad/tags/pull-testing-and-gdbstub-100719-1' into staging

Testing and gdbstub fixes:

  - fix diff-out pass in check-tcg
  - ensure generation of fprem reference
  - fix gdb set_reg fallback

# gpg: Signature made Wed 10 Jul 2019 11:24:28 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-and-gdbstub-100719-1:
  gdbstub: revert to previous set_reg behaviour
  gdbstub: add some notes to the header comment
  tests/tcg: fix diff-out pass to properly report failure
  tests/tcg: fix up test-i386-fprem.ref generation

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