Dawg: Define virtual destructor in .cpp file

This fixes compiler warnings from clang:

src/dict/dawg.h:119:7: warning:
 'Dawg' has no out-of-line virtual method definitions;
 its vtable will be emitted in every translation unit [-Wweak-vtables]

Signed-off-by: Stefan Weil <[email protected]>

Author: stweil

src/dict/dawg.cpp

@@ -42,6 +42,11 @@
 ----------------------------------------------------------------------*/
 namespace tesseract {
 
+// Destructor.
+// It is defined here, so the compiler can create a single vtable
+// instead of weak vtables in every compilation unit.
+Dawg::~Dawg() = default;
+
 bool Dawg::prefix_in_dawg(const WERD_CHOICE &word,
                           bool requires_complete) const {
   if (word.length() == 0) return !requires_complete;

src/dict/dawg.h

@@ -129,7 +129,7 @@ class Dawg {
   inline const STRING &lang() const { return lang_; }
   inline PermuterType permuter() const { return perm_; }
 
-  virtual ~Dawg() = default;
+  virtual ~Dawg();
 
   /// Returns true if the given word is in the Dawg.
   bool word_in_dawg(const WERD_CHOICE &word) const;