Fix compilation of Google Test in C++20 mode

[Godin]

Summary

Without this patch when using CMAKE_CXX_STANDARD=20
and MSVC 19.30.30705.0 compilation of unit tests
fails with

llvm\utils\unittest\googlemock\include\gmock/gmock-actions.h(828): error C2039: 'result_of': is not a member of 'std'

Patch is taken from Google Test:
https://github.com/google/googletest/commit/61f010d703b32de9bfb20ab90ece38ab2f25977f

Do not use std::result_of as it was removed in C++20.

[bkramer]

Thanks

llvm/utils/unittest/googlemock/include/gmock/gmock-actions.h

 };
 
 // Implements the InvokeWithoutArgs(object_ptr, &Class::Method) action.
 template <class Class, typename MethodPtr>
 struct InvokeMethodWithoutArgsAction {
   Class* const obj_ptr;
   const MethodPtr method_ptr;
 
-  using ReturnType = typename std::result_of<MethodPtr(Class*)>::type;
+  using ReturnType =
+      decltype((std::declval<Class*>()->*std::declval<MethodPtr>())());
 
   template <typename... Args>
   ReturnType operator()(const Args&...) const {
     return (obj_ptr->*method_ptr)();
   }
 };
 
 // Implements the IgnoreResult(action) action.