Fix compilation errors

include/audio/dsp_core.hpp

@@ -33,6 +33,7 @@ namespace Audio {
 	  public:
 		enum class Type { Null, Teakra };
 		DSPCore(Memory& mem, Scheduler& scheduler, DSPService& dspService) : mem(mem), scheduler(scheduler), dspService(dspService) {}
+		virtual ~DSPCore() {}
 
 		virtual void reset() = 0;
 		virtual void runAudioFrame() = 0;

include/audio/null_core.hpp

@@ -24,6 +24,7 @@ namespace Audio {
 
 	  public:
 		NullDSP(Memory& mem, Scheduler& scheduler, DSPService& dspService) : DSPCore(mem, scheduler, dspService) {}
+		~NullDSP() override {}
 
 		void reset() override;
 		void runAudioFrame() override;

include/audio/teakra_core.hpp

@@ -75,6 +75,7 @@ namespace Audio {
 
 	  public:
 		TeakraDSP(Memory& mem, Scheduler& scheduler, DSPService& dspService);
+		~TeakraDSP() override {}
 
 		void reset() override;