bison: new external at 2.7.1

Signed-off-by: David Abdurachmanov <David.Abdurachmanov@cern.ch>
flex: new external at 2.5.37

Signed-off-by: David Abdurachmanov <David.Abdurachmanov@cern.ch>
doxygen: new external at 1.8.4

Signed-off-by: David Abdurachmanov <David.Abdurachmanov@cern.ch>