libwebsockets

logs: allow giving log bitfields from cmake to force build or exclusion

By default this doesn't change any existing logging behaviour at all.

But it allows you to define cmake options to force or force-disable the
build of individual log levels using new cmake option bitfields
LWS_LOGGING_BITFIELD_SET and LWS_LOGGING_BITFIELD_CLEAR.

Eg, -DLWS_LOGGING_BITFIELD_SET="(LLL_INFO)" can force INFO log level
built even in release mode.  -DLWS_LOGGING_BITFIELD_CLEAR="(LLL_NOTICE)"
will likewise remove NOTICE logging from the build regardless of
DEBUG or RELEASE mode.