strtod64 function

I've used the 6.1 support for Decimal Floating Point here and there a
year or so but I haven't had any problems until I tried using the
strtod functions today.
When I try to create a C module I get a warning that there's no
prototype for strtod64 even though stdlib.h is included and the parms
are correct. I've also grepped that the prototype is in stdlib:

grep strtod64 /qsys.lib/qsysinc.lib/h.file/stdlib.MBR
_Decimal64 strtod64 ( const char *, char ** );

Basically, I've reduced and reduced my code until it's on the level of
the example in the manual but it still does not work. So I have this:

#include <stdlib.h>
#include <stdio.h>

/* stuff */
char *dfpstring = "3.1415926This stopped it";
char *stopstring;
_Decimal64 dfp;

dfp = strtod64(dfpstring, &stopstring);
printf(" strtod = %Df\n", dfp); /* produces rubbish as the function is
not found */

I'm not using any particular compiler options, I've tried using both
ixlc -c and CRTCMOD as well as strtod128. Anyone have any idea what's
going on?

Best wishes,
Erik