Fix memset, memcpy, memmove calls on Pointer type.

Just note that it's short fix for #4589 only.

src/pointer.cr

@@ -129,6 +129,16 @@ struct Pointer(T)
     (self + offset).value = value
   end
 
+  {% if flag?(:x86_64) %}
+    private def to_size_t(size : Int) : UInt64
+        size.to_u64
+    end
+  {% else %}
+    private def to_size_t(size : Int) : UInt32
+        size.to_u32
+    end
+  {% end %}
+
   # Copies *count* elements from *source* into `self`.
   # If *source* and `self` overlap, behaviour is undefined.
   # Use `#move_from` if they overlap (slower but always works).
@@ -242,7 +252,7 @@ struct Pointer(T)
     raise ArgumentError.new("Negative count") if count < 0
 
     if self.class == source.class
-      Intrinsics.memcpy(self.as(Void*), source.as(Void*), (count * sizeof(T)).to_u32, 0_u32, false)
+      Intrinsics.memcpy(self.as(Void*), source.as(Void*), to_size_t(count * sizeof(T)), 0_u32, false)
     else
       while (count -= 1) >= 0
         self[count] = source[count]
@@ -255,7 +265,7 @@ struct Pointer(T)
     raise ArgumentError.new("Negative count") if count < 0
 
     if self.class == source.class
-      Intrinsics.memmove(self.as(Void*), source.as(Void*), (count * sizeof(T)).to_u32, 0_u32, false)
+      Intrinsics.memmove(self.as(Void*), source.as(Void*), to_size_t(count * sizeof(T)), 0_u32, false)
     else
       if source.address < address
         copy_from source, count
@@ -496,7 +506,7 @@ struct Pointer(T)
   # ```
   def clear(count = 1)
     ptr = self.as(Pointer(Void))
-    Intrinsics.memset(self.as(Void*), 0_u8, (count * sizeof(T)).to_u32, 0_u32, false)
+    Intrinsics.memset(self.as(Void*), 0_u8, to_size_t(count * sizeof(T)), 0_u32, false)
   end
 
   def clone