Fix another is_defined-related bug

It all feel pretty hacked together though... definitely not
confident that I've gotten all of them.

src/codegen/irgen/irgenerator.cpp

@@ -1004,6 +1004,11 @@ class IRGeneratorImpl : public IRGenerator {
                 }
                 prev = val;
                 val->incvref();
+
+                // Clear out the is_defined name since it is now definitely defined:
+                assert(!startswith(name, "!is_defined"));
+                std::string defined_name = _getFakeName("is_defined", name.c_str());
+                _getFake(defined_name, true);
             }
         }
 

test/tests/listcomp.py

-# expected: fail
-
 print [(i, j) for i in range(4) for j in range(4)]
 
 def f():
@@ -20,7 +18,7 @@ f(1, 1)
 # TODO: test on ifs
 
 def f():
-    print [(i, j) for (i, j) in {1:2, 3:4, 5:6, 7:8}.items()]
+    print [(i, j) for (i, j) in sorted({1:2, 3:4, 5:6, 7:8}.items())]
 f()
 
 # The expr should not get evaluated if the if-condition fails:

test/tests/listcomp_assigning.py

-# expected: fail
-
 i = "global"
 def f(n):
     i = "hello"