[ASan][Test-Only] Allow read of size 2 in strcmp.c test (#166179)

Occasionally this test fails on Darwin due to `CHECK: READ of size 1`
not matching the actual output `CHECK: READ of size 2`. This can happen
when the memory before the string `s1` happens to match the first
character of `s2`.

This patch allows for `READ of size 2` to pass in order to account for
the above circumstances.

rdar://151317947

GitOrigin-RevId: 85c78274358717e4d5d019a801decba5c1add484