Where is yyextra on HP-UX 11.11 64-bit?

One of our binaries is using Lex and Yacc functionality. We link it
against libl and liby. However when linking we're getting a warning:
ld: (Warning) Unsatisfied symbol "yyextra" in file /usr/lib/pa20_64/
libl.sl
And when the binary is invoked we get:
/usr/lib/pa20_64/dld.sl: Unsatisfied data symbol 'yyextra' in load
module '/usr/lib/pa20_64/libl.2'
We are on HP-UX 11.11 in 64-bit mode (DA2.0W).
When I apply "what" command to libl.sl and liby.sl I get:
$ what /usr/lib/pa20_64/libl.sl
/usr/lib/pa20_64/libl.sl:
A.11.01.00 HP C LANGUAGE TOOL LIBRARY (LEX) 980815
$ what /usr/lib/pa20_64/liby.sl
/usr/lib/pa20_64/liby.sl:
A.11.01.00 HP C LANGUAGE TOOL LIBRARY (YACC) 980815
If I apply "nm" to libl and grep for yyextra I get it as UNDEF:
$ nm /usr/lib/pa20_64//libl.sl | grep yyextra
[57] | 0| 0|OBJT |GLOB |0| UNDEF|
yyextra
Is there any problem with Lex/Yacc libraries on our machine?

Thanks.

.