C++11: Allow brace initializers in assignment expressions.

Like:
var += {1, 2};
in a function context.

Change-Id: I3936c97c4fcb6b3dcac2979e0508d422d47fddfc
Reviewed-by: hjk <qthjk@ovi.com>

tests/auto/cplusplus/cxx11/data/braceInitializers.1.cpp

@@ -6,3 +6,9 @@ class C {
   Type var1 = {1, 2, 3};
   Type var2{1, 2, 3};
 };
+
+void main() {
+    var1 = {1, 2, {3, 4} };
+    Type var2{{1, 2, 3}, 4};
+    var3 += {1, 2};
+}