CCUtil: Define virtual destructor in .cpp file

This fixes compiler warnings from clang:

src/ccutil/ccutil.h:51:7: warning:
 'CCUtil' has no out-of-line virtual method definitions;
 its vtable will be emitted in every translation unit [-Wweak-vtables]

Signed-off-by: Stefan Weil <sw@weilnetz.de>

src/ccutil/ccutil.cpp

@@ -27,6 +27,11 @@ CCUtil::CCUtil() :
               " whether to adapt to a character", &params_) {
 }
 
+// Destructor.
+// It is defined here, so the compiler can create a single vtable
+// instead of weak vtables in every compilation unit.
+CCUtil::~CCUtil() = default;
+
 CCUtilMutex::CCUtilMutex() {
 #ifdef _WIN32
   mutex_ = CreateMutex(0, FALSE, 0);

src/ccutil/ccutil.h

@@ -51,7 +51,7 @@ class CCUtilMutex {
 class CCUtil {
  public:
   CCUtil();
-  virtual ~CCUtil() = default;
+  virtual ~CCUtil();
 
  public:
   // Read the arguments and set up the data path.