Test and fix the #line outputs.

* tests/atlocal.at (GCC): New.
* tests/synclines.at (AT_TEST_SYNCLINE): New macro.
(Prologue synch line, ,%union synch line, Postprologue synch line)
(Action synch line, Epilogue synch line): New tests.
* src/reader.c (parse_union_decl): Define the muscle stype_line.
* data/bison.simple, data/bison.c++: Use it.

src/reader.c

@@ -759,6 +759,7 @@ parse_union_decl (void)
 
   typed = 1;
 
+  MUSCLE_INSERT_INT ("stype_line", lineno);
   obstack_init (&union_obstack);
   obstack_sgrow (&union_obstack, "union");