ci: Enable C++ modules tests with LLVM/Clang 16.0 on Windows

This works only with the GNU-like front-end and the Ninja generator.

.gitlab/ci/configure_windows_clang_ninja.cmake

@@ -1 +1,5 @@
+if("$ENV{CMAKE_CI_BUILD_NAME}" MATCHES "(^|_)gnu(_|$)")
+  set(CMake_TEST_MODULE_COMPILATION "named,partitions,internal_partitions,export_bmi,install_bmi,shared" CACHE STRING "")
+  set(CMake_TEST_MODULE_COMPILATION_RULES "${CMAKE_CURRENT_LIST_DIR}/cxx_modules_rules_clang.cmake" CACHE STRING "")
+endif()
 include("${CMAKE_CURRENT_LIST_DIR}/configure_windows_clang_common.cmake")