Remove long_u: hashtab: Enable clint: Add to clint.

- Add hashtab.[ch] to clint file.
- Fix clint errors.

clint-files.txt

@@ -9,6 +9,8 @@ src/nvim/api/vim.c
 src/nvim/api/vim.h
 src/nvim/api/window.c
 src/nvim/api/window.h
+src/nvim/hashtab.c
+src/nvim/hashtab.h
 src/nvim/indent.c
 src/nvim/indent.h
 src/nvim/log.c

src/nvim/hashtab.h

@@ -80,4 +80,4 @@ void hash_lock(hashtab_T *ht);
 void hash_unlock(hashtab_T *ht);
 hash_T hash_hash(char_u *key);
 
-#endif /* NVIM_HASHTAB_H */
+#endif  // NVIM_HASHTAB_H