libcdecl: Remove error code argument from cdecl__err.

libcdecl: Remove error code argument from cdecl__err.

All callers of this internal function use the same error code
(CDECL__ENOPARSE), so removing this from the internal interface
can save a little bit of code.

Or at least it would except that this simplification makes GCC
decide to inline yyerror in the parser, which has a significantly
worse opposite effect.  It's not so pretty, but let's mark yyerror
"noinline" as a workaround so that deleting this code actually
results in less code...