sparse reported that several variables and a function were not
forward-declared anywhere and therefore should be 'static'.

Found with sparse by running 'make C=2 CF=-D__CHECK_ENDIAN__ fs/xfs/'
Signed-off-by: NEric Biggers <ebiggers@google.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NDave Chinner <david@fromorbit.com>