ci: add a script to run the tests with an external CMake

.gitlab/ci/configure_external_test.cmake

@@ -0,0 +1,3 @@
+set(CMake_TEST_HOST_CMAKE "ON" CACHE BOOL "")
+
+include("${CMAKE_CURRENT_LIST_DIR}/configure_common.cmake")

.gitlab/ci/ctest_test_external.cmake

@@ -0,0 +1,66 @@
+cmake_minimum_required(VERSION 3.8)
+
+include("${CMAKE_CURRENT_LIST_DIR}/gitlab_ci.cmake")
+
+set(cmake_args
+  -C "${CMAKE_CURRENT_LIST_DIR}/configure_$ENV{CMAKE_CONFIGURATION}.cmake")
+
+# Create an entry in CDash.
+ctest_start(Experimental TRACK "${ctest_track}")
+
+# Gather update information.
+find_package(Git)
+set(CTEST_UPDATE_VERSION_ONLY ON)
+set(CTEST_UPDATE_COMMAND "${GIT_EXECUTABLE}")
+ctest_update()
+
+# Configure the project.
+ctest_configure(
+  OPTIONS "${cmake_args}"
+  RETURN_VALUE configure_result)
+
+# Read the files from the build directory.
+ctest_read_custom_files("${CTEST_BINARY_DIRECTORY}")
+
+# We can now submit because we've configured. This is a cmb-superbuild-ism.
+ctest_submit(PARTS Update)
+ctest_submit(PARTS Configure)
+
+if (configure_result)
+  message(FATAL_ERROR
+    "Failed to configure")
+endif ()
+
+include(ProcessorCount)
+ProcessorCount(nproc)
+
+if (CTEST_CMAKE_GENERATOR STREQUAL "Unix Makefiles")
+  set(CTEST_BUILD_FLAGS "-j${nproc}")
+endif ()
+
+ctest_build(
+  NUMBER_WARNINGS num_warnings
+  RETURN_VALUE build_result)
+ctest_submit(PARTS Build)
+
+if (build_result)
+  message(FATAL_ERROR
+    "Failed to build")
+endif ()
+
+if ("$ENV{CTEST_NO_WARNINGS_ALLOWED}" AND num_warnings GREATER 0)
+  message(FATAL_ERROR
+    "Found ${num_warnings} warnings (treating as fatal).")
+endif ()
+
+include("${CMAKE_CURRENT_LIST_DIR}/ctest_exclusions.cmake")
+ctest_test(
+  PARALLEL_LEVEL "${nproc}"
+  RETURN_VALUE test_result
+  EXCLUDE "${test_exclusions}")
+ctest_submit(PARTS Test)
+
+if (test_result)
+  message(FATAL_ERROR
+    "Failed to test")
+endif ()