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.

tests/Makefile.am

@@ -47,7 +47,8 @@ TESTSUITE_AT = \
 	testsuite.at \
 	input.at \
 	output.at sets.at reduce.at \
-	headers.at actions.at conflicts.at calc.at \
+	synclines.at headers.at actions.at conflicts.at \
+	calc.at \
         torture.at regression.at \
         semantic.at