Merge remote-tracking branch 'remotes/stsquad/tags/pull-testing-and-misc-180121-2' into staging

Testing, gdbstub and semihosting patches:

  - clean-ups to docker images
  - drop duplicate jobs from shippable
  - prettier tag generation (+gtags)
  - generate browsable source tree
  - more Travis->GitLab migrations
  - fix checkpatch to deal with commits
  - gate gdbstub tests on 8.3.1, expand tests
  - support Xfer:auxv:read gdb packet
  - better gdbstub cleanup
  - use GDB's SVE register layout
  - make arm-compat-semihosting common
  - add riscv semihosting support
  - add HEAPINFO, ELAPSED, TICKFREQ, TMPNAM and ISERROR to semihosting

# gpg: Signature made Mon 18 Jan 2021 10:09:11 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-misc-180121-2: (30 commits)
  semihosting: Implement SYS_ISERROR
  semihosting: Implement SYS_TMPNAM
  semihosting: Implement SYS_ELAPSED and SYS_TICKFREQ
  riscv: Add semihosting support for user mode
  riscv: Add semihosting support
  semihosting: Support SYS_HEAPINFO when env->boot_info is not set
  semihosting: Change internal common-semi interfaces to use CPUState *
  semihosting: Change common-semi API to be architecture-independent
  semihosting: Move ARM semihosting code to shared directories
  target/arm: use official org.gnu.gdb.aarch64.sve layout for registers
  gdbstub: ensure we clean-up when terminated
  gdbstub: drop gdbserver_cleanup in favour of gdb_exit
  gdbstub: drop CPUEnv from gdb_exit()
  gdbstub: add support to Xfer:auxv:read: packet
  gdbstub: implement a softmmu based test
  Revert "tests/tcg/multiarch/Makefile.target: Disable run-gdbstub-sha1 test"
  configure: gate our use of GDB to 8.3.1 or above
  test/guest-debug: echo QEMU command as well
  scripts/checkpatch.pl: fix git-show invocation to include diffstat
  gitlab: migrate the minimal tools and unit tests from Travis
  ...

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

# Conflicts:
#	default-configs/targets/riscv32-linux-user.mak
#	default-configs/targets/riscv64-linux-user.mak