As the default option for msvc 2019 does support designated initializers
```
../src/util/tests/timespec_test.cpp(302): error C7555: use of designated initializers requires at least '/std:c++20'
../src/util/tests/timespec_test.cpp(303): error C7555: use of designated initializers requires at least '/std:c++20'
../src/util/tests/timespec_test.cpp(312): error C7555: use of designated initializers requires at least '/std:c++20'
../src/util/tests/timespec_test.cpp(313): error C7555: use of designated initializers requires at least '/std:c++20'
```
Signed-off-by: Yonggang Luo <luoyonggang@gmail.com>
Reviewed-by: Jason Ekstrand <jason.ekstrand@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15497>
To avoid altering any currently existing callers, we continue on with
the calculation regardless of overflow. This also matches the behavior
of GCC's __builtin_add_overflow().
Reviewed-By: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15651>