Merge change from Coreutils.

Merge change from Coreutils.

(read_filesystem_list) [MOUNTED_VMOUNT]: Detect any
error from mntctl.
Use mntctl's return value to drive the entry-processing loop, since
we can't rely on the value of the vmt_length member in the last
entry.  On some systems doing so could result in exhausting
virtual memory.  Based in part on a patch from Mike Jetzer.