add cstdint include

[mo271]

without those includes, I get errors when compiling:

ibex_Cov.h:106:53: error: ‘uint32_t’ has not been declared
  106 |         static void write_pos_int(std::ofstream& f, uint32_t x);

ibex_Cov.cpp:138:9: error: ‘uint32_t’ was not declared in this scope
  138 |         uint32_t x;