XFAIL Linux-only test failure

This already didn't work on 32-bit platforms; now it's not working on 64-bit Linux. Filed as SR-9008.

Author: beccadax

test/SILOptimizer/unused_containers.swift

@@ -5,6 +5,9 @@
 // FIXME: https://bugs.swift.org/browse/SR-7806
 // REQUIRES: CPU=arm64 || CPU=x86_64
 
+// FIXME: https://bugs.swift.org/browse/SR-9008
+// XFAIL: linux
+
 //CHECK-LABEL: @$s17unused_containers16empty_array_testyyF
 //CHECK: bb0:
 //CHECK-NEXT: tuple