Add a FIXME to string.cpp

libs/libc/src/string.cpp

@@ -30,7 +30,7 @@ extern "C"
         return dest;
     }
 
-    char* strncpy(char* dest, const char* src, size_t max)
+    char* strncpy(char* dest, const char* src, size_t max) // FIXME: Implement strncpy according to the specification.
     {
         size_t src_len = strlen(src) + 1; // NULL byte
         memcpy(dest, src, src_len > max ? max : src_len);