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: I738b90855b6b9a8effbf55a468c751b6d0b8edd9
(cherry picked from commit d79ac373483c36f893981c7319d37a5ebbd63b98)