dump: add Windows dump format to dump-guest-memory

dump: add Windows dump format to dump-guest-memory

This patch adds Windows crashdumping feature. Now QEMU can produce ELF-dump
containing Windows crashdump header, which can help to convert to a valid
WinDbg-understandable crashdump file, or immediately create such file.
The crashdump will be obtained by joining physical memory dump and 8K header
exposed through vmcoreinfo/fw_cfg device by guest driver at BSOD time. Option
'-w' was added to dump-guest-memory command. At the moment, only x64
configuration is supported.
Suitable driver can be found at
https://github.com/virtio-win/kvm-guest-drivers-windows/tree/master/fwcfg64

Signed-off-by: Viktor Prutyanov <[email protected]>
Reviewed-by: Marc-André Lureau <[email protected]>
Message-Id: <20180517162342[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>