build: avoid possibly-replaced fprintf in liby-source, yyerror.c

* lib/yyerror.c (yyerror): Use fputs and fputc rather than fprintf
with a mere "%s\n" format.  Always return 0 now, on the assumption
that the return value was never used anyway.
Don't include <config.h> after all.  This avoids a problem
reported by Thiru Ramakrishnan in
http://lists.gnu.org/archive/html/help-bison/2011-11/msg00000.html
* cfg.mk: Exempt lib/yyerror.c from the sc_require_config_h_first test.
* THANKS: Update.
(cherry picked from commit fb9eea8885)

THANKS

@@ -97,6 +97,7 @@ Sergei Steshenko          [email protected]
 Shura                     [email protected]
 Steve Murphy              [email protected]
 Summum Bonum              [email protected]
+Thiru Ramakrishnan        [email protected]
 Tim Josling               [email protected]
 Tim Landscheidt           [email protected]
 Tim Van Holder            [email protected]