Disable clang 16's -Wcast-function-type-strict.

Disable clang 16's -Wcast-function-type-strict.

Clang 16 is still in development, but seawasp reveals that it has
started warning about many of our casts of function pointers (those
introduced by commit 1c27d16e, and some older ones).  Disable the new
warning for now, since otherwise buildfarm animal seawasp fails, and we
have no current plans to change our strategy for these callback function
types.

May be back-patched with other Clang/LLVM 16 changes around release
time.

Discussion: https://postgr.es/m/CA%2BhUKGJvX%2BL3aMN84ksT-cGy08VHErRNip3nV-WmTx7f6Pqhyw%40mail.gmail.com
(cherry picked from commit 101c37cd342a3ae134bb3e5e0abb14ae46692b56)

Author: Thomas Munro <tmunro@postgresql.org>
Author: Alexandra Wang <alexandra.wang.oss@gmail.com>