util: squelch clang cast alignment warning caused by container_of()

src/util.h

@@ -3,6 +3,7 @@
 
 #include <assert.h>
 #include <stddef.h>
+#include <stdint.h>
 
 #include "internal.h"
 
@@ -12,8 +13,10 @@ typedef intptr_t ssize_t;
 
 #define array_count(a) (sizeof(a) / (sizeof((a)[0])))
 
+/* clang-format off */
 #define container_of(ptr, type, member) \
-  ((type*) ((char*) (ptr) -offsetof(type, member)))
+  ((type*) ((uintptr_t) (ptr) - offsetof(type, member)))
+/* clang-format on */
 
 #define unused_var(v) ((void) (v))