[CMake] Don't cache CPPINTEROP_INCLUDE_DIRS and CLING_INCLUDE_DIRS

Cached variables end up in `root-config --config`, and we don't want to
have absolute paths to the bulid directory inside its output.

After this change, no trace of the full ROOT source or build directory
path is left in the output of `root-config --config`.

Closes https://its.cern.ch/jira/browse/ROOT-9481

Author: guitargeek

CMakeLists.txt

@@ -376,6 +376,9 @@ unset(artifact_files)
 
 add_custom_target(move_artifacts DEPENDS ${stamp_file} ${all_artifacts})
 
+if(builtin_cling)
+    set(CLING_INCLUDE_DIRS ${CMAKE_SOURCE_DIR}/interpreter/cling/include)
+endif()
 
 #---Add the main sources ---------------------------------
 add_subdirectory (interpreter)

core/metacling/src/CMakeLists.txt

@@ -50,7 +50,7 @@ target_include_directories(MetaCling SYSTEM PRIVATE
   ${CLANG_INCLUDE_DIRS}
   ${LLVM_INCLUDE_DIRS}
   ${CLAD_INCLUDE_DIRS}
-  ${CPPINTEROP_INCLUDE_DIRS}
+  ${CMAKE_SOURCE_DIR}/interpreter/CppInterOp/include
 )
 
 target_include_directories(MetaCling PRIVATE

interpreter/CMakeLists.txt

@@ -467,8 +467,6 @@ if (builtin_cling)
   add_subdirectory(cling EXCLUDE_FROM_ALL)
   add_dependencies(CLING ${CLING_LIBRARIES})
 
-  set(CLING_INCLUDE_DIRS ${CMAKE_CURRENT_SOURCE_DIR}/cling/include CACHE STRING "")
-
 
 
   #---These are the libraries that we link ROOT with CLING---------------------------
@@ -544,11 +542,6 @@ mark_as_advanced(CLEAR LLVM_ENABLE_ASSERTIONS LLVM_BUILD_TYPE)
 
 ##################### LIBINTEROP ###########################
 
-#---Set InterOp include directories, for any ROOT component that requires the headers--------------------------------------------------------
-set(CPPINTEROP_INCLUDE_DIRS
-  ${CMAKE_CURRENT_SOURCE_DIR}/CppInterOp/include
-  CACHE STRING "CppInterOp include directories.")
-
 #---Set InterOp to build on Cling, this can be toggled to use Clang-REPL-------------------------------------------------------
 set(CPPINTEROP_USE_CLING ON CACHE BOOL "" FORCE)
 set(CPPINTEROP_USE_REPL OFF CACHE BOOL "" FORCE)