Misc: Purge unused code and report startup error to host

src/common/dynamic_library.h

@@ -45,6 +45,9 @@ public:
   /// Returns true if the library was loaded and can be used.
   bool Open(const char* filename, Error* error);
 
+  /// Adopts, or takes ownership of an existing opened library.
+  void Adopt(void* handle);
+
   /// Unloads the library, any function pointers from this library are no longer valid.
   void Close();
 
@@ -61,6 +64,9 @@ public:
     return *ptr != nullptr;
   }
 
+  /// Returns the opaque OS-specific handle.
+  void* GetHandle() const { return m_handle; }
+
   /// Move assignment, transfer ownership.
   DynamicLibrary& operator=(DynamicLibrary&& move);