Fix for SPEC CPU2017 621.wrf_s failure, add missing locking code.

	libgfortran/
	PR libfortran/81195
	* io/unit.c (get_unit): Call __gthread_mutex_lock before newunit_stack
	and newunit_tos references.  Call __gthread_mutex_unlock afterward.

From-SVN: r249667

libgfortran/ChangeLog

+2017-06-26  Jim Wilson  <jim.wilson@r3-a15.aus-colo>
+
+	PR libfortran/81195
+	* io/unit.c (get_unit): Call __gthread_mutex_lock before newunit_stack
+	and newunit_tos references.  Call __gthread_mutex_unlock afterward.
+
 2017-06-24  Thomas Koenig  <tkoenig@gcc.gnu.org>
 
         PR fortran/52473

libgfortran/io/unit.c

@@ -583,14 +583,17 @@ get_unit (st_parameter_dt *dtp, int do_create)
 	}
       else
 	{
+	  __gthread_mutex_lock (&unit_lock);
 	  if (newunit_tos)
 	    {
 	      dtp->common.unit = newunit_stack[newunit_tos].unit_number;
 	      unit = newunit_stack[newunit_tos--].unit;
+	      __gthread_mutex_unlock (&unit_lock);
 	      unit->fbuf->act = unit->fbuf->pos = 0;
 	    }
 	  else
 	    {
+	      __gthread_mutex_unlock (&unit_lock);
 	      dtp->common.unit = newunit_alloc ();
 	      unit = xcalloc (1, sizeof (gfc_unit));
 	      fbuf_init (unit, 128);
@@ -603,12 +606,15 @@ get_unit (st_parameter_dt *dtp, int do_create)
   /* If an internal unit number is passed from the parent to the child
      it should have been stashed on the newunit_stack ready to be used.
      Check for it now and return the internal unit if found.  */
+  __gthread_mutex_lock (&unit_lock);
   if (newunit_tos && (dtp->common.unit <= NEWUNIT_START)
       && (dtp->common.unit == newunit_stack[newunit_tos].unit_number))
     {
       unit = newunit_stack[newunit_tos--].unit;
+      __gthread_mutex_unlock (&unit_lock);
       return unit;
     }
+  __gthread_mutex_unlock (&unit_lock);
 
   /* Has to be an external unit.  */
   dtp->u.p.unit_is_internal = 0;