undefined reference to sbrk

[scole_mail%gmx.com@localhost]

I was trying to cross-compile an ia64 distribution with current on i386.

After adding some stubs to an empty kvm_ia64.c, and adding a fake
_UC_MACHINE_PC(uc) in mcontext.h.  I get this error:

.../src/external/bsd/am-utils/dist/amd/nfs_start.c:69: undefined reference to `sbrk'

I see that is it not defined, but there is an _sbrk

scole@dstar:~/nbsd/src/obj/destdir.ia64/lib> ~/nbsd/src/obj/tooldir.NetBSD-7.0.1_PATCH-i386/ia64--netbsd/bin/nm  -A libc.so |grep sbrk
libc.so:00000000001526f0 T _sbrk

and also there is an ia64 version of of
src/lib/libc/arch/ia64/sys/sbrk.S

What is proper way to fix?  I think ia64 is still using gcc 4.8.5.

Just for reference, here is what my 7.0.1 i386 has 
 scole@dstar:/lib> nm -A libc.so | grep sbrk
 libc.so:000a8bd0 T _sbrk
 libc.so:000a8bd0 W sbrk

Thanks