devel/gnustep-base cannot use ABI=32

[Emmanuel Dreyfus <manu%netbsd.org@localhost>]

With ABI=32 in mk.conf on an amd64 box:
checking for C compiler default output file name... 
configure: error: in `/pkg_comp/obj/pkgsrc/devel/gnustep-base/default/gnustep-base-1.24.0':
configure: error: C compiler cannot create executables
See `config.log' for more details.

The log says:
configure:3727: gcc -O2 -I/usr/pkg/include -I/usr/pkg/share/GNUstep/include -I/u
sr/include -I/usr/pkg/include -I/usr/pkg/share/GNUstep/include -I/usr/include -I
/usr/pkg/include -I/usr/pkg/include -I/usr/pkg/include -L/usr/pkg/lib -L/usr/pkg
/share/GNUstep/lib -Wl,-R/usr/pkg/lib -Wl,-R/usr/pkg/share/GNUstep/lib -L/usr/li
b -Wl,-R/usr/lib -lobjc -lpthread -L/usr/pkg/lib -L/usr/pkg/lib -L/usr/pkg/lib c
onftest.c  >&5
/pkg_comp/obj/pkgsrc/devel/gnustep-base/default/.buildlink/lib/libobjc.so: undefined reference to `__i686.get_pc_thunk.bx'

Note -m32 is missing despite ABI=32. With this I get -m32 set:
ABI=32
CFLAGS += -m32
CXXFLAGS += -m32

But the outcome is the same. The test program is just a void main. 
The problem stems from libobjc. But the file type is correct:
/usr/pkg/lib/libobjc.so.4.6.0: ELF 32-bit LSB shared object, Intel 80386, version 1 (SYSV), dynamically linked, for NetBSD 6.0, stripped

Any idea of what went wrong?

-- 
Emmanuel Dreyfus
manu%netbsd.org@localhost