Include <bits/types.h>

Apparently some freestanding builds need this?

src/core/include/mp-units/ext/prime.h

@@ -32,6 +32,7 @@
 import std;
 #else
 #include <array>
+#include <bits/types.h>
 #include <cstddef>
 #include <cstdint>
 #include <numeric>