Only run on arm architecture

My previous patch failed to only run an arm test on arm architecture.
This adds that condition to the test.

gcc/testsuite/ChangeLog:

2019-02-07  Matthew Malcomson  <matthew.malcomson@arm.com>

	* gcc.dg/rtl/arm/ldrd-peepholes.c: Only run on arm

From-SVN: r268655

gcc/testsuite/ChangeLog

+2019-02-07  Matthew Malcomson  <matthew.malcomson@arm.com>
+
+	* gcc.dg/rtl/arm/ldrd-peepholes.c: Only run on arm
+
 2019-02-07  Andreas Krebbel  <krebbel@linux.ibm.com>
 
 	* gcc.target/s390/zvector/xl-xst-align-1.c: New test.

gcc/testsuite/gcc.dg/rtl/arm/ldrd-peepholes.c

-/* { dg-do compile } */
+/* { dg-do compile { target arm*-*-* } } */
 /* { dg-skip-if "Ensure only targetting arm with TARGET_LDRD" { *-*-* } { "-mthumb" } { "" } } */
 /* { dg-options "-O3 -marm -fdump-rtl-peephole2" } */