Merge remote-tracking branch 'remotes/stsquad/tags/pull-testing-and-gdbstub-170320-1' into staging

Testing and gdbstub updates:

  - docker updates for VirGL
  - re-factor gdbstub for static GDBState
  - re-factor gdbstub for dynamic arrays
  - add SVE support to arm gdbstub
  - add some guest debug tests to check-tcg
  - add aarch64 userspace register tests
  - remove packet size limit to gdbstub
  - simplify gdbstub monitor code
  - report vContSupported in gdbstub to use proper single-step

# gpg: Signature made Tue 17 Mar 2020 17:47:46 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-and-gdbstub-170320-1: (28 commits)
  gdbstub: Fix single-step issue by confirming 'vContSupported+' feature to gdb
  gdbstub: do not split gdb_monitor_write payload
  gdbstub: change GDBState.last_packet to GByteArray
  tests/tcg/aarch64: add test-sve-ioctl guest-debug test
  tests/tcg/aarch64: add SVE iotcl test
  tests/tcg/aarch64: add a gdbstub testcase for SVE registers
  tests/guest-debug: add a simple test runner
  configure: allow user to specify what gdb to use
  tests/tcg/aarch64: userspace system register test
  target/arm: don't bother with id_aa64pfr0_read for USER_ONLY
  target/arm: generate xml description of our SVE registers
  target/arm: default SVE length to 64 bytes for linux-user
  target/arm: explicitly encode regnum in our XML
  target/arm: prepare for multiple dynamic XMLs
  gdbstub: extend GByteArray to read register helpers
  target/i386: use gdb_get_reg helpers
  target/m68k: use gdb_get_reg helpers
  target/arm: use gdb_get_reg helpers
  gdbstub: add helper for 128 bit registers
  gdbstub: move mem_buf to GDBState and use GByteArray
  ...

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