gtest: fix std::is_trivially_copy_constructible for GCC 4.8 & 4.9 properly
gtest: fix std::is_trivially_copy_constructible for GCC 4.8 & 4.9 properly

`std::is_pod<T>` was deprecated in C++20

original (pre `is_pod`) error on GCC 4.8:
```
/fmt/test/gtest/gtest.h: In static member function 'static constexpr bool testing::internal::MatcherBase<T>::IsInlined()':
/fmt/test/gtest/gtest.h:6512:12: error: 'is_trivially_copy_constructible' was not declared in this scope
            std::is_trivially_copy_constructible<M>::value &&
            ^
/fmt/test/gtest/gtest.h:6512:45: error: expected primary-expression before '>' token
            std::is_trivially_copy_constructible<M>::value &&
                                                  ^
/fmt/test/gtest/gtest.h:6512:46: error: '::value' has not been declared
            std::is_trivially_copy_constructible<M>::value &&
                                                   ^
```

alabuzhev/fmt,alabuzhev/fmt,cppformat/cppformat,cppformat/cppformat,alabuzhev/fmt,cppformat/cppformat