boot loader: Always show 4 GB memory limit safemode option

On x86 we mainly want to disable PAE, which is now also used with less
memory as long as NX support is available. Ideally we'd check this
condition as well and only add the menu item, if the kernel would
enable PAE.

src/system/boot/loader/menu.cpp

@@ -1135,8 +1135,12 @@ add_safe_mode_menu()
 		}
 	}
 
-	// ... add the menu, if so
-	if (hasMemoryBeyond4GB) {
+	bool needs64BitPaging = true;
+		// TODO: Determine whether 64 bit paging (i.e. PAE for x86) is needed
+		// for other reasons (NX support).
+
+	// ... add the menu item, if so
+	if (hasMemoryBeyond4GB || needs64BitPaging) {
 		safeMenu->AddItem(
 			item = new(nothrow) MenuItem("Ignore memory beyond 4 GiB"));
 		item->SetData(B_SAFEMODE_4_GB_MEMORY_LIMIT);