MutableIterator: Define virtual destructor in .cpp file

This fixes compiler warnings from clang:

src/ccmain/mutableiterator.h:44:7: warning:
 'MutableIterator' 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/ccmain/Makefile.am

@@ -55,6 +55,7 @@ libtesseract_main_la_SOURCES = \
   fixxht.cpp \
   linerec.cpp \
   ltrresultiterator.cpp \
+  mutableiterator.cpp \
   output.cpp \
   pageiterator.cpp \
   pagesegmain.cpp \

src/ccmain/mutableiterator.cpp

@@ -0,0 +1,24 @@
+///////////////////////////////////////////////////////////////////////
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+///////////////////////////////////////////////////////////////////////
+
+#include "mutableiterator.h"
+
+namespace tesseract {
+
+// Destructor.
+// It is defined here, so the compiler can create a single vtable
+// instead of weak vtables in every compilation unit.
+MutableIterator::~MutableIterator() = default;
+
+}  // namespace tesseract.

src/ccmain/mutableiterator.h

@@ -51,7 +51,7 @@ class MutableIterator : public ResultIterator {
       : ResultIterator(
           LTRResultIterator(page_res, tesseract, scale, scaled_yres, rect_left,
                             rect_top, rect_width, rect_height)) {}
-  virtual ~MutableIterator() = default;
+  virtual ~MutableIterator();
 
   // See PageIterator and ResultIterator for most calls.