Adjust overflow for invariants in bounds_of_var_in_loop.

Adjust overflow for invariants in bounds_of_var_in_loop.

Invariants returned from SCEV can have TREE_OVERFLOW set.  Clear the
overflow as we do with the rest of the values returned from this
function.

gcc/ChangeLog:

	* gimple-range.cc (gimple_ranger::range_of_ssa_name_with_loop_info):
	Remove TREE_OVERFLOW special case.
	* vr-values.c (bounds_of_var_in_loop): Adjust overflow for
	invariants.