Merging r321777:

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r321777 | rsmith | 2018-01-03 17:02:18 -0800 (Wed, 03 Jan 2018) | 2 lines

PR35028: Retain duplicate alignas attributes in template instantiation.

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git-svn-id: https://llvm.org/svn/llvm-project/cfe/branches/release_60@322676 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/Basic/Attr.td

@@ -549,6 +549,7 @@ def Aligned : InheritableAttr {
                                           Keyword<"_Alignas">]>,
                    Accessor<"isDeclspec",[Declspec<"align">]>];
   let Documentation = [Undocumented];
+  let DuplicatesAllowedWhileMerging = 1;
 }
 
 def AlignValue : Attr {

test/SemaTemplate/alignas.cpp

@@ -21,3 +21,14 @@ struct C { char a[16]; };
 
 static_assert(sizeof(my_union<A, B, C>) == 16, "");
 static_assert(alignof(my_union<A, B, C>) == 8, "");
+
+namespace PR35028 {
+  template<class X, int Alignment> struct alignas(X) alignas(long long) alignas(long double) alignas(Alignment) Aligned {
+    union {
+      long long align1;
+      long double align2;
+      char data[sizeof(X)];
+    };
+  };
+  Aligned<int, 1> a;
+}