Add two helpers to ensure people won't ignore some edge cases such as
pointers overflowing the address space.

Also fix #8924 to some degree, the amount of unchecked alignForward is
still scary.

Revert "tests: disable i386-linux-gnu -lc target due to CI failures"

This reverts commit 97a2f4e7ae9c52c595841347bb0b26572b180dcf.