Fix compilation errors in support/lockedpool.cpp

Changes in #12048 cause a compilation error in Arena::walk() when
ARENA_DEBUG is defined. Specifically, Arena's chunks_free map was
changed to have a different value type.

Additionally, missing includes cause other compilation errors when
ARENA_DEBUG is defined.

Reproduced with:

make CPPFLAGS=-DARENA_DEBUG

src/support/lockedpool.cpp

@@ -23,6 +23,10 @@
 #endif
 
 #include <algorithm>
+#ifdef ARENA_DEBUG
+#include <iomanip>
+#include <iostream>
+#endif
 
 LockedPoolManager* LockedPoolManager::_instance = nullptr;
 std::once_flag LockedPoolManager::init_flag;
@@ -149,7 +153,7 @@ void Arena::walk() const
         printchunk(chunk.first, chunk.second, true);
     std::cout << std::endl;
     for (const auto& chunk: chunks_free)
-        printchunk(chunk.first, chunk.second, false);
+        printchunk(chunk.first, chunk.second->first, false);
     std::cout << std::endl;
 }
 #endif