When yydebug, report semantic and location values for reductions.

* data/glr.c (yy_reduce_print): Report the semantic values and the
locations.
(YY_REDUCE_PRINT): Adjust.
(yyglrReduce): Use them.
(b4_rhs_value, b4_rhs_location): Remove m4_eval invocations.
* data/c.m4 (b4_yysymprint_generate): Specify the const arguments.
* tests/calc.at (_AT_CHECK_CALC_ERROR): Remove the reduction
traces.

tests/calc.at

@@ -409,6 +409,7 @@ sed '/^Starting/d
 /^Error:/d
 /^Next/d
 /^Discarding/d
+/ \$[[0-9$]]* = /d
 /^yydestructor:/d' stderr >at-stderr
 mv at-stderr stderr
 # 2. Create the reference error message.