ENH: Variable CTK_SUPERBUILD_BINARY_DIR is now defined in CMakeLists.txt

In case CTK is built using SuperBuild, within CTK project ...
  CTK_SUPERBUILD_BINARY_DIR : .../Projects/CTK-Superbuild
  CTK_BINARY_DIR : .../Projects/CTK-Superbuild/CTK-build

In case CTK is NOT built using SuperBuild, within CTK project ...
  CTK_SUPERBUILD_BINARY_DIR : .../Projects/CTK-Build
  CTK_BINARY_DIR : .../Projects/CTK-Build

Note also that before SuperBuild.cmake is included,
  CTK_SUPERBUILD_BINARY_DIR is equal to CTK_BINARY_DIR

CMakeLists.txt

@@ -333,6 +333,15 @@ IF(CTK_SUPERBUILD)
 ENDIF()
 
 #-----------------------------------------------------------------------------
+# CTK_SUPERBUILD_BINARY_DIR
+
+# If CTK_SUPERBUILD_BINARY_DIR isn't defined, it means CTK is *NOT* build using Superbuild.
+# In that specific case, CTK_SUPERBUILD_BINARY_DIR should default to CTK_BINARY_DIR
+IF(NOT DEFINED CTK_SUPERBUILD_BINARY_DIR)
+  SET(CTK_SUPERBUILD_BINARY_DIR ${CTK_BINARY_DIR})
+ENDIF()
+
+#-----------------------------------------------------------------------------
 # Set C/CXX Flags
 #
 SET(CMAKE_CXX_FLAGS ${CTK_CXX_FLAGS})

SuperBuild.cmake

@@ -324,6 +324,7 @@ ExternalProject_Add(${proj}
     ${ctk_superbuild_boolean_args}
     -DCTK_SUPERBUILD:BOOL=OFF
     -DCTEST_USE_LAUNCHERS:BOOL=${CTEST_USE_LAUNCHERS}
+    -DCTK_SUPERBUILD_BINARY_DIR:PATH=${CTK_BINARY_DIR}
     -DWITH_COVERAGE:BOOL=${WITH_COVERAGE}
     -DCMAKE_INSTALL_PREFIX:PATH=${ep_install_dir}
     -DCMAKE_BUILD_TYPE:STRING=${CMAKE_BUILD_TYPE}