tree-opt: Fix bootstrap failure in tree-ssa-forwprop.c some more PR90838

2020-01-13  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/90838
	* tree-ssa-forwprop.c (simplify_count_trailing_zeroes): Use
	SCALAR_INT_TYPE_MODE directly in CTZ_DEFINED_VALUE_AT_ZERO macro
	argument rather than to initialize temporary for targets that
	don't use the mode argument at all.  Initialize ctzval to avoid
	warning at -O0.