We should use these (internal) functions in libsigrok exclusively from
now on, i.e. no more use of glib's g_debug() etc.
These functions are only for libsigrok, the frontends use whatever
logging mechanism is suitable there.
Until now the build would break if the user doesn't enable at least one
of the libusb1.0-based LAs. I.e., you could not compile only OLS, or
only the demo driver.
Uwe Hermann