tree-optimization/116290 - fix compare-debug issue in ldist

tree-optimization/116290 - fix compare-debug issue in ldist

Loop distribution does different analysis with -g0/-g due to counting
a debug stmt starting a BB against a limit which will everntually
lead to different IVOPTs choices.  I've fixed a possible IVOPTs
issue on the way even though it doesn't make a difference here.

	PR tree-optimization/116290
	* tree-loop-distribution.cc (determine_reduction_stmt_1): PHIs
	have no debug variants.  Start with first non-debug real stmt.
	* tree-ssa-loop-ivopts.cc (find_givs_in_bb): Do not analyze
	debug stmts.

	* gcc.dg/pr116290.c: New testcase.