q(u)int128 isn't supported with clang using MSVC's STL

Although building with clang(-cl) isn't supported, clang-cl is used by clangd under the hood on Windows in projects that compile with MSVC. When including any header that transitively includes qtypes.h, clangd errors with In included file: static assertion failed due to requirement 'std::is_signed_v<__int128>': Qt requires <type_traits> and <limits> to work for q(u)int128. This is because MSVC's STL (which clang-cl uses) doesn't support 128bit integers.