- cmake: sync some picky gcc warnings with autotools.
- cmake, autotools: add `-Wold-style-definition` for clang too.
- cmake: more precise version info for old clang options.
- cmake: use `IN LISTS` syntax in `foreach()`.
Reviewed-by: Daniel Stenberg
Reviewed-by: Marcel Raad
Closes#12324
033f8e2a08