[AArch64] Add REQUIRES: aarch64-registered-target to aarch64-targetattr-arch.c. NFC

Author: davemgreen

clang/test/CodeGen/aarch64-targetattr-arch.c

@@ -1,6 +1,7 @@
 // RUN: %clang_cc1 -triple aarch64-eabi -target-feature +v8a -verify -DHAS8 -S %s -o -
 // RUN: %clang_cc1 -triple aarch64-eabi -target-feature +v8.1a -verify -DHAS81 -S %s -o -
 // RUN: %clang_cc1 -triple aarch64-eabi -target-feature +v9a -verify -DHAS9 -S %s -o -
+// REQUIRES: aarch64-registered-target
 
 #ifdef HAS9
 // expected-no-diagnostics