Copying of overlapping memory regions is undetected

[lzaoral]

Symbiotic does not detect UB when the memory regions of arguments of memcpy, strcpy or strncpy overlap. This should be quite an easy fix as we just need to add some additional asserts to corresponding implementations in lib/libc (Divine does practically the same thing).

Tests: https://github.com/aufover/aufover-benchmark/tree/main/tests/single-c/mem-overlap

[mchalupa]

Yep, you are right.