Misc: Make struct member functions file-local

src/util/cd_image_ecm.cpp

@@ -158,6 +158,8 @@ static void eccedc_generate(u8* sector, int type)
   }
 }
 
+namespace {
+
 class CDImageEcm : public CDImage
 {
 public:
@@ -216,6 +218,8 @@ private:
   CDSubChannelReplacement m_sbi;
 };
 
+} // namespace
+
 CDImageEcm::CDImageEcm() = default;
 
 CDImageEcm::~CDImageEcm()