Fix addition/overflow checks.

For unsigned arithmetic, use:

(a + b < a) to detect whether a+b wraps
(a > c / b) to detect whether a*b > c

Bug: 120078455
Test: builds and boots
Change-Id: Ic4f4d44f7c0656caa115f90f4cfa130192914949
(cherry picked from commit da2f2fd0)