Make Genode::Thread's attribute accesible in child classes.

src/mx/memory/reclamation/epoch_manager.h

@@ -57,7 +57,7 @@ private:
  * every local epoch is greater than the epoch
  * when the resource is deleted.
  */
-class EpochManager : Genode::Thread
+class EpochManager : public Genode::Thread
 {
 public:
     EpochManager(const std::uint16_t count_channels, dynamic::Allocator &allocator,

src/mx/tasking/worker.h

@@ -18,7 +18,7 @@ namespace mx::tasking {
 /**
  * The worker executes tasks from his own channel, until the "running" flag is false.
  */
-class alignas(64) Worker : Genode::Thread
+class alignas(64) Worker : public Genode::Thread
 {
 public:
     Worker(std::uint16_t id, std::uint16_t target_core_id, std::uint16_t target_numa_node_id,