backedges (ana/backedge.h) and to represent loops
  (ana/irloop.h).  The scc algorithm (ana/irscc.c) builds
  both datastructures.
  The algorithm does not yet work properly for interprocedural
  graphs.  Finds more loops than only recursions.

  Improved place_code: now moves nodes out of loops.
  Fixed bug in iropt.c:  wrong parameter in debug info: iropt_dbg.c
  Now flag set_opt_control_flow can be set to 1 again.

[r457]