/usr/pkgsrc/filesystems/fs-utils fail to build on Arch Linux x86_64

[Jens Staal <staal1978%gmail.com@localhost>]

I tried setting up Rump on Arch linux following the instructions at:
http://www.netbsd.org/~stacktic/rumpabroad.html

pkgsrc version:
https://aur.archlinux.org/packages/netbsd-pkgsrc/
updated with cvs update -A -dP today

Rump built fine after symlinking /usr/lib to /usr/lib64

fs-utils does however fail giving this message:

[...]
all ===> bin/fsu_cat
gcc -L/usr/pkgsrc/filesystems/fs-utils/work/libnbcompat -L/usr/pkg/lib -Wl,-
R/usr/pkg/lib -Wl,-rpath=/usr/pkg/lib -L../../../libnbcompat -L/usr/pkg/lib -
lnbcompat -lc -ldl  -o fsu_cat fsu_cat.o -L../../../libnbcompat -L/usr/pkg/lib 
-lnbcompat -lc -ldl -L../../lib/libfsu_mount -lfsu_mount -
L../../lib/libfsu_utils -lfsu_utils -L/usr/pkg/lib -lukfs -lrumpuser -lutil -
lpthread -lrumpvfs -lrump
/usr/pkgsrc/filesystems/fs-utils/work/.buildlink/lib/librump.so: undefined 
reference to `__builtin_stdarg_start'
collect2: error: ld returned 1 exit status
*** Error code 1

Stop.
bmake: stopped in /usr/pkgsrc/filesystems/fs-utils/work/fs-utils/bin/fsu_cat
*** Error code 1

Stop.
bmake: stopped in /usr/pkgsrc/filesystems/fs-utils/work/fs-utils/bin
*** Error code 1

Stop.
bmake: stopped in /usr/pkgsrc/filesystems/fs-utils/work/fs-utils
*** Error code 1

Stop.
bmake: stopped in /usr/pkgsrc/filesystems/fs-utils
*** Error code 1

Stop.
bmake: stopped in /usr/pkgsrc/filesystems/fs-utils 


... so it seems like __builtin_stdarg_start in the Rump libraries is not 
working on Linux. Some googling indicate that it might be a GCC issue.
Anyone got some hints on how to solve it?