Ok, doing a little preliminary work, I can't find any non-free licenses in the current release per their own LICENSE.txt and gpl-3.0-exceptions.txt files. Now there could be a incompatible mix of FOSS licenses but I could use a an expert here...
Looking at the licenses that licensecheck recognizes I get this:
$ licensecount .
9682 *No copyright* UNKNOWN
741 *No copyright* GENERATED FILE
489 GPL (v3 or later)
218 UNKNOWN
69 LGPL (v2.1 or later) (with incorrect FSF address)