Always rebuild a DeclRefExpr if its FoundDecl would change.

Fixes a regression introduced by r369999.

llvm-svn: 373022
diff --git a/clang/test/SemaTemplate/using-decl.cpp b/clang/test/SemaTemplate/using-decl.cpp
new file mode 100644
index 0000000..1ef2a2d
--- /dev/null
+++ b/clang/test/SemaTemplate/using-decl.cpp
@@ -0,0 +1,16 @@
+// RUN: %clang_cc1 -std=c++2a -verify %s
+// expected-no-diagnostics
+
+namespace UsingInGenericLambda {
+  namespace a {
+    enum { b };
+  }
+  template<typename> void c() {
+    auto d = [](auto) {
+      using a::b;
+      (void)b;
+    };
+    d(0);
+  }
+  void e() { c<int>(); }
+}