Avoid remounting already mounted /run and /tmp directories

Adds the function fistmpfs to determine if a new tmpfs mount should be
performed on /run and /tmp. The function supports cases where more
complex mount hierarchies are in use, including overlayfs backed mounts.

Signed-off-by: Mathias Thore <mathias.thore@atlascopco.com>

src/util.h

@@ -80,6 +80,7 @@ void  de_dotdot    (char *file);
 
 int   ismnt        (char *file, char *dir, char *mode);
 int   fismnt       (char *dir);
+int   fistmpfs     (char *dir);
 
 #ifdef HAVE_TERMIOS_H
 int     ttinit     (void);