DynamicLoader: Update test to avoid using CMAKE_INTDIR

Pass our own definition using `$<CONFIG>` instead.

CMakeLists.txt

@@ -1038,6 +1038,10 @@ if(KWSYS_STANDALONE OR CMake_SOURCE_DIR)
     set_property(TARGET ${KWSYS_NAMESPACE}TestsCxx PROPERTY CXX_INCLUDE_WHAT_YOU_USE "")
     set_property(TARGET ${KWSYS_NAMESPACE}TestsCxx PROPERTY LABELS ${KWSYS_LABELS_EXE})
     target_link_libraries(${KWSYS_NAMESPACE}TestsCxx ${KWSYS_TARGET_LINK})
+    get_property(_isMultiConfig GLOBAL PROPERTY GENERATOR_IS_MULTI_CONFIG)
+    if(_isMultiConfig)
+      set_property(TARGET ${KWSYS_NAMESPACE}TestsCxx APPEND PROPERTY COMPILE_DEFINITIONS BUILD_CONFIG="$<CONFIG>")
+    endif()
 
     set(TEST_SYSTEMTOOLS_SOURCE_DIR "${CMAKE_CURRENT_SOURCE_DIR}")
     set(TEST_SYSTEMTOOLS_BINARY_DIR "${CMAKE_CURRENT_BINARY_DIR}")

testDynamicLoader.cxx

@@ -53,9 +53,9 @@ static std::string GetLibName(const char* lname, const char* subdir = nullptr)
     slname += "/";
     slname += subdir;
   }
-#ifdef CMAKE_INTDIR
+#ifdef BUILD_CONFIG
   slname += "/";
-  slname += CMAKE_INTDIR;
+  slname += BUILD_CONFIG;
 #endif
   slname += "/";
   slname += kwsys::DynamicLoader::LibPrefix();