CCStruct: Define virtual destructor in .cpp file

This fixes compiler warnings from clang:

src/ccstruct/ccstruct.h:25:7: warning:
 'CCStruct' 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/ccstruct/ccstruct.cpp

@@ -28,4 +28,9 @@ const double CCStruct::kAscenderFraction = 0.25;
 const double CCStruct::kXHeightCapRatio = CCStruct::kXHeightFraction /
     (CCStruct::kXHeightFraction + CCStruct::kAscenderFraction);
 
+// Destructor.
+// It is defined here, so the compiler can create a single vtable
+// instead of weak vtables in every compilation unit.
+CCStruct::~CCStruct() = default;
+
 }

src/ccstruct/ccstruct.h

@@ -25,7 +25,7 @@ namespace tesseract {
 class CCStruct : public CUtil {
  public:
   CCStruct() = default;
-  ~CCStruct() = default;
+  virtual ~CCStruct();
 
   // Globally accessible constants.
   // APPROXIMATIONS of the fractions of the character cell taken by