blktap/fs-back: Build fixes for Fedora 13

blktap/fs-back: Build fixes for Fedora 13

1. Some files use stat, mkfifo, mkdir etc. without including
sys/stat.h

2. Some programs link against libpthread without a -lpthread compile
option. The compile used to work if this library happened to be used
by one of the other libraries that was being linked against, but
Fedora 13 has stopped allowing this.

From: M A Young <m.a.young@durham.ac.uk>
Signed-off-by: Keir Fraser <keir.fraser@citrix.com>