Improve DSE which in turn eliminates the need for jump threading and block duplication for the original testcase in pr89689 which in turn eliminates the false positive -Warray-bounds warning for the original testcase.

	PR tree-optimization/89689
	* builtins.def (BUILT_IN_OBJECT_SIZE): Make it const rather than pure.

	PR tree-optimization/89689
	* gcc.dg/pr89689.c: New test.