Firmware BMP with ENABLE_DEBUG=1 will print WARN and INFO as before.
PC-Hosted BMPwill alway print to stderr. Warn is printed unconditional,
INFO, GDB, TARGET, DONGLE and WIRE will print if their appropriate bit in
cl_debuglevel is set via the -v verbose command line argument.
INFO will go to stdout with -t or -l.
As libusb has no real async callback, we need to call libusb_handle_events()
in different places. While waiting for the gdb connection, we set the
socket to non-blocking and check additional for usb events in that loop. That
way, detach is also detected while waiting for connection. With debugger
attached, SET_IDLE_STATE ist missused for checking for usb events.
