Thread safety analysis: make sure that expressions in attributes are parsed
in an unevaluated context.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@174644 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Parse/ParseDecl.cpp b/lib/Parse/ParseDecl.cpp
index 8e24a14..14fd581 100644
--- a/lib/Parse/ParseDecl.cpp
+++ b/lib/Parse/ParseDecl.cpp
@@ -1023,6 +1023,7 @@
 
   // now parse the list of expressions
   while (Tok.isNot(tok::r_paren)) {
+    EnterExpressionEvaluationContext Unevaluated(Actions, Sema::Unevaluated);
     ExprResult ArgExpr(ParseAssignmentExpression());
     if (ArgExpr.isInvalid()) {
       ArgExprsOk = false;