autoconf: AC_MSG_CHECKING consistency

Make the wording more consistent for the kernel AC_MSG_CHECKING
output (e.g. "checking whether ...".). Additionally, group some
of the VFS interface checks with the others. No functional change.

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Attila Fülöp <attila@fueloep.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #13529