implement the alias attirbute (in both Sema and Codegen)

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@52092 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Parse/AttributeList.cpp b/lib/Parse/AttributeList.cpp
index c99722c..8697d4e 100644
--- a/lib/Parse/AttributeList.cpp
+++ b/lib/Parse/AttributeList.cpp
@@ -56,6 +56,9 @@
     if (!memcmp(Str, "pure", 4)) return AT_pure;
     if (!memcmp(Str, "mode", 4)) return AT_mode;
     break;
+  case 5:
+    if (!memcmp(Str, "alias", 5)) return AT_alias;
+    break;
   case 6:
     if (!memcmp(Str, "packed", 6)) return AT_packed;
     if (!memcmp(Str, "malloc", 6)) return AT_malloc;