Port to Forte Developer 7 C compiler.

Port to Forte Developer 7 C compiler.
(struct YYLTYPE): If locations are not being used, declare a single
dummy member, as empty structs do not conform to the C standard.
(YYERROR, YYBACKUP): Do not use "do { ...; return foo; } while (0)";
the Forte Developer 7 C compiler complains that end-of-loop
code is not reached.