Sema: Don't crash when trying to emit a precedence warning on postinc/decrement.

Post-Inc can occur as a binary call (the infamous dummy int argument), but it's
not really a binary operator.

Fixes PR15628.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@178412 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/SemaExpr.cpp b/lib/Sema/SemaExpr.cpp
index 62bfa3c..75da99c 100644
--- a/lib/Sema/SemaExpr.cpp
+++ b/lib/Sema/SemaExpr.cpp
@@ -5412,7 +5412,8 @@
     // Make sure this is really a binary operator that is safe to pass into
     // BinaryOperator::getOverloadedOpcode(), e.g. it's not a subscript op.
     OverloadedOperatorKind OO = Call->getOperator();
-    if (OO < OO_Plus || OO > OO_Arrow)
+    if (OO < OO_Plus || OO > OO_Arrow ||
+        OO == OO_PlusPlus || OO == OO_MinusMinus)
       return false;
 
     BinaryOperatorKind OpKind = BinaryOperator::getOverloadedOpcode(OO);