bsd.sys.mk: for clang >= 19, similar to gcc >= 8.1, turn off -Werror for
-Wcast-function-type-mismatch.

PR: 280562
Approved by: re (kib)
MFC after: 1 month

(cherry picked from commit d575077527d448ee45b923fa8c6b0cb7216ca5c5)
(cherry picked from commit de45d36ffb604798c22f7ee556d774490902c1e1)