Tests/RunCMake/CXXModules: add a test for issue #25112

Add a test case for C++ `OBJECT` libraries providing modules to
consumers.

Tests/RunCMake/CXXModules/RunCMakeTest.cmake

@@ -142,6 +142,7 @@ string(REPLACE "," ";" CMake_TEST_MODULE_COMPILATION "${CMake_TEST_MODULE_COMPIL
 if ("named" IN_LIST CMake_TEST_MODULE_COMPILATION)
   run_cxx_module_test(simple)
   run_cxx_module_test(library library-static -DBUILD_SHARED_LIBS=OFF)
+  run_cxx_module_test(object-library)
   run_cxx_module_test(generated)
   run_cxx_module_test(deep-chain)
   run_cxx_module_test(duplicate)

Tests/RunCMake/CXXModules/examples/object-library-stderr.txt

@@ -0,0 +1,4 @@
+CMake Warning \(dev\) at CMakeLists.txt:[0-9]* \(target_sources\):
+  CMake's C\+\+ module support is experimental.  It is meant only for
+  experimentation and feedback to CMake developers.
+This warning is for project developers.  Use -Wno-dev to suppress it.

Tests/RunCMake/CXXModules/examples/object-library/CMakeLists.txt

@@ -0,0 +1,22 @@
+cmake_minimum_required(VERSION 3.24)
+project(cxx_modules_objlib CXX)
+
+include("${CMAKE_SOURCE_DIR}/../cxx-modules-rules.cmake")
+
+add_library(objlib OBJECT)
+target_sources(objlib
+  PUBLIC
+    FILE_SET CXX_MODULES
+      BASE_DIRS
+        "${CMAKE_CURRENT_SOURCE_DIR}"
+      FILES
+        importable.cxx)
+target_compile_features(objlib PUBLIC cxx_std_20)
+
+add_executable(objmain)
+target_sources(objmain
+  PRIVATE
+    main.cxx)
+target_link_libraries(objmain PRIVATE objlib)
+
+add_test(NAME objmain COMMAND objmain)

Tests/RunCMake/CXXModules/examples/object-library/importable.cxx

@@ -0,0 +1,6 @@
+export module importable;
+
+export int from_import()
+{
+  return 0;
+}

Tests/RunCMake/CXXModules/examples/object-library/main.cxx

@@ -0,0 +1,6 @@
+import importable;
+
+int main(int argc, char* argv[])
+{
+  return from_import();
+}