tree-optimization/109849 - fix fallout of PRE hoisting change

tree-optimization/109849 - fix fallout of PRE hoisting change

The PR109849 fix made us no longer hoist some memory loads because
of the expression set intersection.  We can still avoid to compute
the union by simply taking the first sets expressions and leave
the pruning of expressions with values not suitable for hoisting
to sorted_array_from_bitmap_set.

	PR tree-optimization/109849
	* tree-ssa-pre.cc (do_hoist_insertion): Do not intersect
	expressions but take the first sets.

	* gcc.dg/tree-ssa/ssa-hoist-9.c: New testcase.