[FreeBSD] Fix strict compile (maintainer mode) build breakage in vc_generic.c

This commit fixes following strict compile errors on freebsd7.2 platform:
..src/libntirpc/src/vc_generic.c: In function 'svc_readv_vc':
..src/libntirpc/src/vc_generic.c:287: warning: implicit declaration of function 'readv'
..src/libntirpc/src/vc_generic.c: In function 'svc_writev_vc':
..src/libntirpc/src/vc_generic.c:313: warning: implicit declaration of function 'writev'

Signed-off-by: Sachin Bhamare <sbhamare@panasas.com>
[FreeBSD] Fix strict compile build breakage in xdr_vrec.c

gcc (GCC) 4.2.1 20070719  [FreeBSD] throws following warning due to the double
declaration of xdr_vrec_noop function.
warning: 'xdr_vrec_noop' declared 'static' but never defined

Removing one of the declaration which doesn't specify 'unused' attribute fixes
the warning/error.

Signed-off-by: Sachin Bhamare <sbhamare@panasas.com>