yysyntax_error: more preparation for readability of next patch.

yysyntax_error: more preparation for readability of next patch.

There are no behavioral changes here.
* data/glr.c (yyreportSyntaxError): Reorganize.
* data/lalr1.cc (yy::parser::yysyntax_error_): Reorganize.
* tests/conflicts.at (%error-verbose and consistent errors):
Reorganize.
(cherry picked from commit 25a648d8a6a00bb810844e375d0d15125ed7eaf8)

Conflicts:

	tests/conflicts.at