tree-optimization/112636 - estimate niters before header copying

The following avoids a mismatch between an early query for maximum
number of iterations of a loop and a late one when through ranger
we'd get iterations estimated.  Instead make sure we compute niters
before querying the iteration bound.

	PR tree-optimization/112636
	* tree-ssa-loop-ch.cc (ch_base::copy_headers): Call
	estimate_numbers_of_iterations before querying
	get_max_loop_iterations_int.
	(pass_ch::execute): Initialize SCEV and loops appropriately.

	* gcc.dg/pr112636.c: New testcase.