libfrog: add wrappers for listmount and statmount

libfrog: add wrappers for listmount and statmount

Add some wrappers for listmount and statmount so that we don't have to
open-code the kernel ABI quirks in every utility program that uses it.
Note that glibc seems to have discussed providing a wrapper in late 2023
but took no action; and the listmount manpage says that there is no
glibc wrapper.

Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>