ask cmake for per-configuration output subdir

On single-configuration build systems as Makefile Generators, there is
no subdirectory for the configuration in the build tree - therefore ask
cmake for the subdir by using CMAKE_CFG_INTDIR, which is just '.' on
single-configuration build systems (Linux et al.).

googletest/cmake/internal_utils.cmake

@@ -245,7 +245,7 @@ function(py_test name)
       add_test(
         NAME ${name}
         COMMAND ${PYTHON_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/test/${name}.py
-            --build_dir=${CMAKE_CURRENT_BINARY_DIR}/$<CONFIGURATION>)
+            --build_dir=${CMAKE_CURRENT_BINARY_DIR}/${CMAKE_CFG_INTDIR})
     else (${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION} GREATER 3.1)
       add_test(
         ${name}