Conflict with st_dev/st_ino identifiers under Debian GNU/Hurd

The problem is that the struct file_status on UNIX systems has two
members called st_dev and st_ino; those are also members of the
struct stat, and they are reserved identifiers which can also be
provided as #define (and this is the case for st_dev on Hurd).
The solution (attached) is to rename them, for example adding a
"fs_" prefix (= file status) to them.

Patch by Pino Toscano

llvm-svn: 155354