clang: Define NO_WDEPRECATED_NON_PROTOTYPE for clang 15

[imp]

Summary

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

[jhb]

share/mk/bsd.sys.mk

120

I would put this here maybe? I think in most other places we tend to sort these lists by compiler type first then version, so:

clang 14
clang 15
clang 16
...
gcc 10
gcc 11
gcc 12
...

[imp]

share/mk/bsd.sys.mk

120

I was totally confused by your comment, and thought I'd get back to it later...
But I totally agree. You've found a mismerge I think.

[imp]

move, per review