hashlib: Add missing stdint.h include

We use `uint32_t` `uint64_t` etc. so add an explicit include.

kernel/hashlib.h

@@ -17,6 +17,8 @@
 #include <string>
 #include <vector>
 
+#include <stdint.h>
+
 namespace hashlib {
 
 const int hashtable_size_trigger = 2;