EquationDetectBase: Define virtual destructor in .cpp file

This fixes compiler warnings from clang:

src/textord/equationdetectbase.h:32:7: warning:
 'EquationDetectBase' 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/textord/equationdetectbase.cpp

@@ -23,6 +23,11 @@
 
 namespace tesseract {
 
+// Destructor.
+// It is defined here, so the compiler can create a single vtable
+// instead of weak vtables in every compilation unit.
+EquationDetectBase::~EquationDetectBase() = default;
+
 void EquationDetectBase::RenderSpecialText(Pix* pix,
                                            BLOBNBOX* blob) {
   ASSERT_HOST(pix != nullptr && pixGetDepth(pix) == 32 && blob != nullptr);

src/textord/equationdetectbase.h

@@ -32,7 +32,7 @@ class ColPartitionSet;
 class EquationDetectBase {
  public:
   EquationDetectBase() = default;
-  virtual ~EquationDetectBase() = default;
+  virtual ~EquationDetectBase();
 
   // Iterate over the blobs inside to_block, and set the blobs that we want to
   // process to BSTT_NONE. (By default, they should be BSTT_SKIP). The function