[AArch64] Add v8.1a architecture

Add support for AArch64 v8.1 architecture. Briefly it is described on http://community.arm.com/groups/processors/blog/2014/12/02/the-armv8-a-architecture-and-its-ongoing-development

Reviewers: jmolloy

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D8493

llvm-svn: 235110
diff --git a/clang/lib/Driver/Tools.cpp b/clang/lib/Driver/Tools.cpp
index fda4106..3053d9b 100644
--- a/clang/lib/Driver/Tools.cpp
+++ b/clang/lib/Driver/Tools.cpp
@@ -1802,8 +1802,17 @@
                                 const ArgList &Args,
                                 std::vector<const char *> &Features) {
   std::pair<StringRef, StringRef> Split = March.split("+");
-  if (Split.first != "armv8-a")
+
+  if (Split.first == "armv8-a" ||
+      Split.first == "armv8a") {
+    // ok, no additional features.
+  } else if (
+      Split.first == "armv8.1-a" ||
+      Split.first == "armv8.1a" ) {
+    Features.push_back("+v8.1a");
+  } else {
     return false;
+  }
 
   if (Split.second.size() && !DecodeAArch64Features(D, Split.second, Features))
     return false;