core-deps-3.[4,6]: fix musicbrainz build

Backported a patch from libmusicbrainz SVN.

[  6%] Building CXX object src/CMakeFiles/musicbrainz4.dir/Query.cc.o
/run/media/elmarco/320g/src/gnome/libmusicbrainz-4.0.0/src/Query.cc: In member function 'void MusicBrainz4::CQuery::WaitRequest() const':
/run/media/elmarco/320g/src/gnome/libmusicbrainz-4.0.0/src/Query.cc:295:19: error: 'usleep' was not declared in this scope

https://bugzilla.gnome.org/show_bug.cgi?id=674007