Fixes for CMake Google Test on Windows

Also make use of fetch content

CMakeLists.txt

@@ -137,13 +137,34 @@ if(OPENDDS_BUILD_EXAMPLES OR OPENDDS_BUILD_TESTS)
   add_subdirectory(DevGuideExamples/DCPS/Messenger)
 endif()
 if(OPENDDS_BUILD_TESTS)
-  find_package(GTest QUIET)
+  find_package(GTest QUIET PATHS "${OPENDDS_GTEST}")
   if(NOT GTest_FOUND)
-    message("GTest not found, falling back to local copy")
+    set(gtestsm "${OPENDDS_SOURCE_DIR}/tests/googletest")
+    if(EXISTS "${gtestsm}/CMakeLists.txt")
+      message("GTest not found, using submodule")
+      set(fetch_args SOURCE_DIR "${gtestsm}")
+    else()
+      message("GTest not found, using clone")
+      set(fetch_args
+        GIT_REPOSITORY "https://github.com/OpenDDS/googletest"
+        GIT_TAG "v1.8.x"
+        GIT_SHALLOW TRUE
+        GIT_PROGRESS TRUE
+        USES_TERMINAL_DOWNLOAD TRUE
+      )
+    endif()
+    FetchContent_Declare(googletest ${fetch_args})
     # Prevent overriding the parent project's compiler/linker
     # settings on Windows
     set(gtest_force_shared_crt ON CACHE BOOL "" FORCE)
-    add_subdirectory(tests/googletest)
+    FetchContent_MakeAvailable(googletest)
+  endif()
+  if(TARGET GTest::gtest)
+    get_target_property(google_test_bin_dir GTest::gtest BINARY_DIR)
+    set(_OPENDDS_GOOGLE_TEST_DIR "${google_test_bin_dir}" CACHE INTERNAL "")
+  elseif(TARGET gtest)
+    get_target_property(google_test_bin_dir gtest BINARY_DIR)
+    set(_OPENDDS_GOOGLE_TEST_DIR "${google_test_bin_dir}" CACHE INTERNAL "")
   endif()
 
   add_subdirectory(tests/cmake/ace_tao_only)

cmake/opendds_testing.cmake

@@ -27,6 +27,13 @@ function(opendds_add_test)
   else()
     set(env_var_name LD_LIBRARY_PATH)
   endif()
+  if(DEFINED _OPENDDS_GOOGLE_TEST_DIR)
+    _opendds_path_list(lib_dir_list APPEND "${_OPENDDS_GOOGLE_TEST_DIR}")
+    if(CMAKE_CONFIGURATION_TYPES)
+      _opendds_path_list(lib_dir_list APPEND
+        "${_OPENDDS_GOOGLE_TEST_DIR}$<$<BOOL:$<CONFIG>>:/$<CONFIG>>")
+    endif()
+  endif()
   _opendds_path_list(lib_dir_list "$ENV{${env_var_name}}" "${TAO_LIB_DIR}")
   foreach(lib_dir "${OPENDDS_LIB_DIR}" ${arg_EXTRA_LIB_DIRS})
     _opendds_path_list(lib_dir_list APPEND "${lib_dir}")