Try disabling unity builds and removing warning errors

Author: raulcd

cpp/cmake_modules/ThirdpartyToolchain.cmake

@@ -3409,8 +3409,20 @@ function(build_google_cloud_cpp_storage)
   set(GOOGLE_CLOUD_CPP_ENABLE_WERROR OFF)
   set(GOOGLE_CLOUD_CPP_WITH_MOCKS OFF)
   set(BUILD_TESTING OFF)
+  # Unity build causes some build errors.
+  set(CMAKE_UNITY_BUILD FALSE)
   fetchcontent_makeavailable(google_cloud_cpp)
 
+  # Disable -Wdocumentation-deprecated-sync warning for google-cloud-cpp.
+  if(CMAKE_CXX_COMPILER_ID MATCHES "Clang")
+    foreach(_target google-cloud-cpp::storage google-cloud-cpp::rest_internal
+                    google-cloud-cpp::common)
+      if(TARGET ${_target})
+        target_compile_options(${_target} INTERFACE -Wno-documentation-deprecated-sync)
+      endif()
+    endforeach()
+  endif()
+
   # Remove unused directories to save build directory storage.
   # 141MB -> 79MB
   file(REMOVE_RECURSE "${google_cloud_cpp_SOURCE_DIR}/ci")