Include src/training when exporting compile commands with cmake

`cmake -DCMAKE_EXPORT_COMPILE_COMMANDS=ON ..` is used to get the file
compile_commands.json which is required by clang-tidy.

Export compile commands for all source files, not only those from
the default build, so clang-tidy can cover all source files.

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

CMakeLists.txt

@@ -233,6 +233,9 @@ include_directories(src/opencl)
 include_directories(src/textord)
 include_directories(src/viewer)
 include_directories(src/wordrec)
+if(CMAKE_EXPORT_COMPILE_COMMANDS)
+include_directories(src/training)
+endif()
 
 ########################################
 # LIBRARY tesseract