AK+Kernel+LibELF: Remove the need for IteratorDecision::Continue

By constraining two implementations, the compiler will select the best
fitting one. All this will require is duplicating the implementation and
simplifying for the `void` case.

This constraining also informs both the caller and compiler by passing
the callback parameter types as part of the constraint
(e.g.: `IterationFunction<int>`).

Some `for_each` functions in LibELF only take functions which return
`void`. This is a minimal correctness check, as it removes one way for a
function to incompletely do something.

There seems to be a possible idiom where inside a lambda, a `return;` is
the same as `continue;` in a for-loop.

Kernel/Arch/x86/CPU.h

@@ -8,6 +8,7 @@
 
 #include <AK/Atomic.h>
 #include <AK/Badge.h>
+#include <AK/Concepts.h>
 #include <AK/Noncopyable.h>
 #include <AK/Vector.h>
 
@@ -733,7 +734,7 @@ public:
 
     static size_t processor_count() { return processors().size(); }
 
-    template<typename Callback>
+    template<IteratorFunction<Processor&> Callback>
     static inline IterationDecision for_each(Callback callback)
     {
         auto& procs = processors();
@@ -745,6 +746,16 @@ public:
         return IterationDecision::Continue;
     }
 
+    template<VoidFunction<Processor&> Callback>
+    static inline IterationDecision for_each(Callback callback)
+    {
+        auto& procs = processors();
+        size_t count = procs.size();
+        for (size_t i = 0; i < count; i++)
+            callback(*procs[i]);
+        return IterationDecision::Continue;
+    }
+
     ALWAYS_INLINE u8 physical_address_bit_width() const { return m_physical_address_bit_width; }
 
     ALWAYS_INLINE ProcessorInfo& info() { return *m_info; }