gnu: diffutils: Skip some tests on all powerpc architectures.

This is a follow-up to e3fbaeee13.

* gnu/packages/base.scm (diffutils)[arguments]: When building for any
powerpc architecture add make-flags to mark 2 tests as failed.

Change-Id: Iceea5bbb045b10f704da4783abd8bf244941e793

gnu/packages/base.scm

@@ -374,7 +374,7 @@ differences.")
                 #~'("XFAIL_TESTS=test-year2038"))
                ;; TODO: Figure out why these gnulib tests are failing.
                ((and (not (%current-target-system))
-                     (target-ppc64le?))
+                     (target-powerpc?))
                 #~'("XFAIL_TESTS=test-float-h large-subopt"))
                (else
                 #~'()))