clang: Define NO_WDEPRECATED_NON_PROTOTYPE for clang 15

Clang 15 enforces function definitions using the C89 form rather than
the K&R form. While not strictly a prototype (which is only for a
declaration), use the name that mirror's clang's warning name. Much code
in contrib still uses K&R function definitions, so invent this for
compiling there.

Sponsored by: Netflix
Reviewed by: jhb
Differential Revision: https://reviews.freebsd.org/D37515