%merge: delegate the generation of calls to mergers to m4

Don't generate C code from bison, leave that to the skeletons.

* src/output.c (merger_output): Emit invocations to b4_call_merger.
* data/skeletons/glr.c (b4_call_merger): New.

data/skeletons/glr.c

@@ -1,4 +1,4 @@
-                                                                    -*- C -*-
+#                                                             -*- C -*-
 
 # GLR skeleton for Bison
 
@@ -145,6 +145,15 @@ m4_define([b4_rhs_location],
 [(b4_rhs_data([$1], [$2]).yyloc)])
 
 
+# b4_call_merger(MERGER-NUM, MERGER-NAME, SYMBOL-SUM)
+# ---------------------------------------------------
+m4_define([b4_call_merger],
+[b4_case([$1],
+         [    b4_symbol_if([$3], [has_type],
+                           [yy0->b4_symbol($3, type) = $2 (*yy0, *yy1);],
+                           [*yy0 = $2 (*yy0, *yy1);])])])
+
+
 ## -------------- ##
 ## Declarations.  ##
 ## -------------- ##