Fixed visibility of undeclared functions and objects.

test/err/bug2304-var-use.c

@@ -0,0 +1,15 @@
+/* Bug 2304 - Visibility of objects/functions undeclared in file scope but 'extern'-declared in unrelated block scopes */
+
+void f1(void)
+{
+    extern int a;
+}
+
+/* 'a' is still invisible in the file scope */
+
+int main(void)
+{
+    return a * 0;   /* Usage of 'a' should be an error */
+}
+
+int a = 42;