tree-optimization/104716 - check if we can copy loop in loop distribution

tree-optimization/104716 - check if we can copy loop in loop distribution

The following checks whether we can copy the loop before attempting
to do so in loop distribution.  In the testcase there's a computed
goto and thus abnormal edges which we cannot redirect.

2022-03-01  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/104716
	* tree-loop-distribution.cc (find_seed_stmts_for_distribution):
	Check if we can copy the loop.

	* gfortran.dg/pr104716.f: New testcase.