Merge remote-tracking branch 'remotes/stsquad/tags/pull-testing-gdbstub-docs-080221...

Merge remote-tracking branch 'remotes/stsquad/tags/pull-testing-gdbstub-docs-080221-1' into staging

Testing, gdbstub and doc tweaks:

  - increase timeout on replay kernel acceptance test
  - fixes for binfmt_misc docker images
  - better gdb version detection
  - don't silently skip gdb tests
  - fix for gdbstub auxv handling
  - cleaner handling of check-tcg on tcg disabled builds
  - expand vexpress/versitile docs with examples

# gpg: Signature made Mon 08 Feb 2021 11:12:03 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-testing-gdbstub-docs-080221-1:
  docs/system: document an example booting the versatilepb machine
  docs/system: document an example vexpress-a15 invocation
  tests/Makefile.include: don't use TARGET_DIRS for check-tcg
  scripts/mtest2make.py: export all-%s-targets variable and use it
  tests/tcg: Replace /bin/true by true (required on macOS)
  gdbstub: Fix handle_query_xfer_auxv
  tests/tcg: don't silently skip the gdb tests
  configure: bump the minimum gdb version for check-tcg to 9.1
  configure: make version_ge more tolerant of shady version input
  tests/docker: add a docker-exec-copy-test
  tests/docker: alias docker-help target for consistency
  tests/docker: preserve original name when copying libs
  tests/docker: make _copy_with_mkdir accept missing files
  tests/docker: Fix typo in help message
  tests/docker: Fix _get_so_libs() for docker-binfmt-image
  tests/acceptance: Increase the timeout in the replay tests

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