gem_close_race: Fix linker flags

Seems the -lpthread was missed in
commit 8f771f3facae133bb72216fa05c74bc817920b6d
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Tue Oct 29 14:21:29 2013 +0000

    gem_close_race: Also test random closing of active fd

Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
1 file changed