Adds an implementation for stpcpy and stpncpy, which are posix extension
Not sure if this is a valid argument for mempcpy. As in, we might want mempcpy to be instrumented really.
Nit: Instead of initializing to 0 here, do it in the for statement ...
... like this:
for (i = 0; ...)
Nit: This can be
size_t end = i;
Can this for loop be replaced with a call to bzero?