qemu: Create a gdbserver to UNIX socket bridge

Infix ships with a gdbserver configuration that listens on
/dev/hvc1. Connect this to gdbserver.sock on the host, so that we can
attach to or run Infix processes using GDB.

qemu/qemu.sh

@@ -135,6 +135,8 @@ run_qemu()
 	  -display none -rtc base=utc,clock=vm \
 	  -device virtio-serial -chardev stdio,mux=on,id=console0 \
 	  -device virtconsole,chardev=console0 -mon chardev=console0 \
+	  -chardev socket,id=gdbserver,path=gdbserver.sock,server=on,wait=off \
+	  -device virtconsole,name=console1,chardev=gdbserver \
 	  $(loader_args) \
 	  $(rootfs_args) \
 	  $(rw_args) \