Add OS_PATH_SEPARATOR for platforms which have different path separator characters (e.g. Windows and 'classic' MacOS).

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/os/os.h b/os/os.h
index d6ce9a7..cbb476f 100644
--- a/os/os.h
+++ b/os/os.h
@@ -125,6 +125,10 @@
 #define FIO_PREFERRED_ENGINE	"sync"
 #endif
 
+#ifndef FIO_OS_PATH_SEPARATOR
+#define FIO_OS_PATH_SEPARATOR	"/"
+#endif
+
 #ifndef FIO_MAX_JOBS
 #define FIO_MAX_JOBS		2048
 #endif