Roll forward fix of global var shadow detection

RELNOTES[INC]: Skylark: It is an error to shadow a global variable with a local variable after the global has already been accessed in the function.

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MOS_MIGRATED_REVID=130014492

src/test/java/com/google/devtools/build/lib/syntax/FunctionTest.java

diff --git a/src/test/java/com/google/devtools/build/lib/syntax/FunctionTest.java b/src/test/java/com/google/devtools/build/lib/syntax/FunctionTest.java
index d5d3937..3451238 100644
--- a/src/test/java/com/google/devtools/build/lib/syntax/FunctionTest.java
+++ b/src/test/java/com/google/devtools/build/lib/syntax/FunctionTest.java
@@ -120,6 +120,18 @@
   }
 
   @Test
+  public void testFunctionDefLocalVariableReferencedInCallBeforeAssignment() throws Exception {
+    checkEvalErrorContains("Variable 'a' is referenced before assignment.",
+        "def dummy(x):",
+        "  pass",
+        "a = 1",
+        "def func():",
+        "  dummy(a)",
+        "  a = 2",
+        "func()\n");
+  }
+
+  @Test
   public void testFunctionDefLocalVariableReferencedAfterAssignment() throws Exception {
     eval("a = 1",
         "def func():",