arc: Use @pcl assembler syntax instead of invalid expressions

The old ARC assembler would accept expressions like 'LABEL-(.&-4)'
which would calculate the offset from the PCL to LABEL.  The new ARC
assembler does not accept these expressions, instead there's an @pcl
synax, used like LABEL@pcl which gives the offset from PCL to LABEL.

Most of the use of the old expression syntax have been removed,
however, this one got missed.

gcc/ChangeLog:

	* config/arc/arc.md (doloop_begin_i): Use @pcl assembler syntax.

From-SVN: r246932

gcc/ChangeLog

+2017-04-14  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	* config/arc/arc.md (doloop_begin_i): Use @pcl assembler syntax.
+
 2017-04-14  Michael Meissner  <meissner@linux.vnet.ibm.com>
 
 	PR target/80098

gcc/config/arc/arc.md

@@ -5070,7 +5070,7 @@
     {
       /* ??? Can do better for when a scratch register
 	 is known.  But that would require extra testing.  */
-      return "push_s r0\;add r0,pcl,%4-(.&-4)\;sr r0,[2]; LP_START\;add r0,pcl,.L__GCC__LP%1-(.&-4)\;sr r0,[3]; LP_END\;pop_s r0";
+      return "push_s r0\;add r0,pcl,%4@pcl\;sr r0,[2]; LP_START\;add r0,pcl,.L__GCC__LP%1@pcl\;sr r0,[3]; LP_END\;pop_s r0";
     }
   /* Check if the loop end is in range to be set by the lp instruction.  */
   size = INTVAL (operands[3]) < 2 ? 0 : 2048;