Without the change build fails on `gcc-13` as:
$ nix build --impure --expr 'with import ./. {}; cm256cc.override { stdenv = gcc13Stdenv; }' -L
...
/build/source/unit_test/data.h:37:9: error: 'uint16_t' does not name a type
37 | uint16_t i;
| ^~~~~~~~
/build/source/unit_test/data.h:33:1: note: 'uint16_t' is defined in header '<cstdint>'; this is probably fixable by adding '#include <cstdint>'
32 | #include <string.h>
+++ |+#include <cstdint>
