[iwyu] Add missing includes

R=titzer@chromium.org

Change-Id: I26261e16a9db2b4b9622b1d4a3eab959fa24b7e3
Reviewed-on: https://chromium-review.googlesource.com/713496
Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48489}

src/reglist.h

@@ -5,6 +5,10 @@
 #ifndef V8_REGLIST_H_
 #define V8_REGLIST_H_
 
+#include <cstdint>
+
+#include "src/base/bits.h"
+
 namespace v8 {
 namespace internal {