Few updates after testing on OpenSUSE Tumbleweed (#1 )

* fstest: fix compilation by adding missing header

fstat() declaration is available on sys/stat.h, include
this header to fix compilation on modern systems.

Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>

* make configure executable

Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>

* Update build instructions

The old instructions clearly did not work.

Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>

38953a2