AArch64: re-enable tests that were looking for a non-existent backend.

In the final phase of the merge, I managed to disable a bunch of Clang
tests accidentally. Fortunately none of them seem to have broken in
the interim.

llvm-svn: 211149
diff --git a/clang/test/CodeGen/arm64-crc32.c b/clang/test/CodeGen/arm64-crc32.c
index a1c447a..37ced18 100644
--- a/clang/test/CodeGen/arm64-crc32.c
+++ b/clang/test/CodeGen/arm64-crc32.c
@@ -1,4 +1,4 @@
-// REQUIRES: arm64-registered-target
+// REQUIRES: aarch64-registered-target
 // RUN: %clang_cc1 -triple arm64-none-linux-gnu \
 // RUN:   -O3 -S -emit-llvm -o - %s | FileCheck %s