Eliminate old-style function declarations

Eliminate old-style function declarations

The C2x standard removes support for non-prototype function
declarations, and clang 15 issues warnings for them
(https://reviews.llvm.org/D122895).  Add -Werror=strict-prototypes to
the build and fix all of the non-prototype declarations and
definitions.

For RPC code, try to be consistent with libtirpc and recent *BSD
versions of rpcgen.  This includes casting each time a concrete
function is used as an xdrproc_t value, since each XDR per-type
function accepts a different object pointer type.  A few invocations
of xdrproc_t values pass a third argument with value LASTUNSIGNED,
even though XDR per-type functions accept only two parameters.
libtirpc has removed these third arguments; do so here as well.

[ghudson@mit.edu: added -Werror=strict-prototypes and fixed
declarations it breaks under gcc and clang; added xdrproc_t changes;
rewrote commit message; style changes]