Add support for the C11 _Alignof keyword.

This behaves like the existing GNU __alignof and C++11 alignof keywords;
most of the patch is simply adding the third token spelling to various places.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@159494 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/SemaCodeComplete.cpp b/lib/Sema/SemaCodeComplete.cpp
index 5cab990..ff83324 100644
--- a/lib/Sema/SemaCodeComplete.cpp
+++ b/lib/Sema/SemaCodeComplete.cpp
@@ -1955,6 +1955,19 @@
       AddObjCExpressionResults(Results, true);
     }
 
+    if (SemaRef.getLangOpts().C11) {
+      // _Alignof
+      Builder.AddResultTypeChunk("size_t");
+      if (SemaRef.getASTContext().Idents.get("alignof").hasMacroDefinition())
+        Builder.AddTypedTextChunk("alignof");
+      else
+        Builder.AddTypedTextChunk("_Alignof");
+      Builder.AddChunk(CodeCompletionString::CK_LeftParen);
+      Builder.AddPlaceholderChunk("type");
+      Builder.AddChunk(CodeCompletionString::CK_RightParen);
+      Results.AddResult(Result(Builder.TakeString()));
+    }
+
     // sizeof expression
     Builder.AddResultTypeChunk("size_t");
     Builder.AddTypedTextChunk("sizeof");