Include missing `cstring` header in autotester.cpp

[melvyn2]

memcpy is used but the relevant header wasn't included, causing the file not to compile:

../../tests/autotester/autotester.cpp: In lambda function:
../../tests/autotester/autotester.cpp:180:25: error: ‘memcpy’ was not declared in this scope
  180 |                         memcpy(temp_buffer_dup, temp_buffer, param.size);
      |                         ^~~~~~
../../tests/autotester/autotester.cpp:28:1: note: ‘memcpy’ is defined in header ‘<cstring>’; did you forget to ‘#include <cstring>’?
   27 | #include "autotester.h"
  +++ |+#include <cstring>
   28 | 
make: *** [Makefile:1417: autotester.o] Error 1

[adriweb]

Hm, I should clean up this part anyway :)