GTest: Move to using FetchContent instead of an in-tree copy

thirdparty/CMakeLists.txt

@@ -41,7 +41,7 @@ if(BUILD_TESTING)
     adios2_add_thirdparty_target(gtest GTest::GTest)
   else()
     add_subdirectory(GTest)
-    adios2_add_thirdparty_target(gtest gtest_interface)
+    adios2_add_thirdparty_target(gtest gtest)
   endif()
 endif()
 

thirdparty/GTest/CMakeLists.txt

@@ -1,22 +1,16 @@
 message_start_thirdparty()
 
-set(BUILD_GTEST ON CACHE INTERNAL "")
-set(BUILD_GMOCK OFF CACHE INTERNAL "")
-if(BUILD_SHARED_LIBS)
-  set(gtest_force_shared_crt ON CACHE INTERNAL "")
-endif()
-set(BUILD_SHARED_LIBS OFF)
-
-set(CMAKE_POLICY_DEFAULT_CMP0042 NEW)
-
-add_subdirectory(googletest EXCLUDE_FROM_ALL)
-
-add_library(gtest_interface INTERFACE)
-target_link_libraries(gtest_interface INTERFACE gtest)
-if(BUILD_SHARED_LIBS)
-  target_compile_definitions(gtest_interface INTERFACE
-    GTEST_LINKED_AS_SHARED_LIBRARY=1
-  )
-endif()
+include(FetchContent)
+FetchContent_Declare(
+  googletest
+  GIT_REPOSITORY https://github.com/google/googletest.git
+  GIT_TAG        release-1.10.0
+  CMAKE_ARGS
+    -DBUILD_GTEST=ON
+    -DBUILD_GMOCK=OFF
+    -DBUILD_SHARED_LIBS=OFF
+    -Dgtest_force_shared_crt=${BUILD_SHARED_LIBS}
+)
+FetchContent_MakeAvailable(googletest)
 
 message_end_thirdparty()