This updates a few warnings that were diagnosing no arguments for a
`...` variadic macro parameter as a GNU extension when it actually is a
C++20/C23 extension now.
This fixes#84495.
C++20 and later allow you to pass no argument for the ... parameter in
a variadic macro, whereas earlier language modes and C disallow it.
We no longer diagnose in C++20 and later modes. This fixes PR51609.