Loop distribution fix for SCC detection

The following adjusts data_dep_in_cycle_p to properly consider the
whole loop nest when looking for data dep cycles and exempting
zero-distance DDRs instead of just the outermost loop.

	* tree-loop-distribution.cc (loop_distribution::data_dep_in_cycle_p):
	Consider all loops in the nest when looking for
	lambda_vector_zerop.