Fixed block-scope extern declarations visibility.

Fixed missing file-scope static function codegen output in a rare care.

test/val/extern.c

@@ -0,0 +1,31 @@
+/* Test for shadowing and linkage of file-scope "static" and block-scope "extern" declarations */
+
+static int g(int x);            /* Generated functions with internal linkage are not always kept in cc65 */
+
+int main(void)
+{
+    char f = 'f';               /* Shadows global "int f(void)" (if any) */
+    char c = 'c';               /* Shadows global "int c" (if any) */
+    {
+        void* f = 0;            /* Shadows local  "char f" */
+        void* c = 0;            /* Shadows local  "char c" */
+        {
+            int f(void);        /* Shadows local  "char f" and "void* f" */
+            extern int g(int);  /* Shadows global "int g(int x)" */
+            extern int c;       /* Shadows local  "char c" and "void* c" */
+            return f() ^ g(c);  /* Link to global "int g(int x)" */
+        }
+    }
+}
+
+int c = 42;
+
+int f(void)
+{
+    return 42;
+}
+
+int g(int x)
+{
+    return x;
+}