add expr/decl ambiguity test

From-SVN: r21825

gcc/testsuite/g++.old-deja/g++.brendan/parse3.C

+// Build don't link: 
+
+// these are marked as expected errors because they evidence an
+// ambiguity in the grammar between expressions and declarations.
+// when the parser's been cleaned up or rewritten, these two error
+// markers can go away, since they'll no longer occur.
+
+class A
+{
+  public:
+    int high;
+    unsigned int low;
+    A operator+(const A in);
+};
+
+A A::operator+(const A in)
+{
+    if (high==0)
+      return A();    // this works
+    else
+      return (A());  // this works not !! -> why ?? // ERROR - 
+} // ERROR -