Make iteration type explicit, this is very important here.

Summary: We need to be very careful in this part of the code as to where things are copied, or dereferenced.

Test Plan:
  ninja check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D11439

src/radix.h

@@ -252,7 +252,9 @@ template <typename T> struct RadixTree {
     void forEachLeaf(RadixElement e, Callable &&func) const {
         if (e.isNode()) {
             e.getNode()->forEachChild(
-                [&](auto pElement) { forEachLeaf(pElement->load(), func); });
+                [&](const std::atomic<RadixElement> *pElement) {
+                    forEachLeaf(pElement->load(), func);
+                });
             return;
         }