gdbstub refactor:

  - split user and softmmu code
  - use cleaner headers for tb_flush, target_ulong
  - probe for gdb multiarch support at configure
  - make syscall handling target independent
  - add update guest debug of accel ops

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# gpg: Good signature from "Alex Bennée (Master Work Key) <alex.bennee@linaro.org>" [full]
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* tag 'pull-gdbstub-070323-3' of https://gitlab.com/stsquad/qemu

: (30 commits)
  gdbstub: move update guest debug to accel ops
  gdbstub: Build syscall.c once
  stubs: split semihosting_get_target from system only stubs
  gdbstub: Adjust gdb_do_syscall to only use uint32_t and uint64_t
  gdbstub: Remove gdb_do_syscallv
  gdbstub: split out softmmu/user specifics for syscall handling
  include: split target_long definition from cpu-defs
  testing: probe gdb for supported architectures ahead of time
  gdbstub: only compile gdbstub twice for whole build
  gdbstub: move syscall handling to new file
  gdbstub: move register helpers into standalone include
  gdbstub: don't use target_ulong while handling registers
  gdbstub: fix address type of gdb_set_cpu_pc
  gdbstub: specialise stub_can_reverse
  gdbstub: introduce gdb_get_max_cpus
  gdbstub: specialise target_memory_rw_debug
  gdbstub: specialise handle_query_attached
  gdbstub: abstract target specific details from gdb_put_packet_binary
  gdbstub: rationalise signal mapping in softmmu
  gdbstub: move chunks of user code into own files
  ...

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