A search on the mail archive shows that something similar happens at
regular intervals, but I couldn't deduce the solution... (groff is correctly
linked using c++)

Sep 24 15:57 GMT cvs, Sep 18 i386 userland
newfs /usr/obj, mount /usr/obj
find /usr/src -name obj.i386 -type l | xargs rm
build.sh -E build

and:

mkdir src/roff/groff
c++ -I. -I/usr/src/gnu/dist/groff/src/roff/groff  -I/usr/src/tools/groff/obj.i386/build/src/include -I/usr/src/gnu/dist/groff/src/include -DHAVE_CONFIG_H -O  -c /usr/src/gnu/dist/groff/src/roff/groff/groff.cpp
cc -I. -I/usr/src/gnu/dist/groff/src/roff/groff  -I/usr/src/tools/groff/obj.i386/build/src/include -I/usr/src/gnu/dist/groff/src/include -DHAVE_CONFIG_H -O  -c /usr/src/gnu/dist/groff/src/roff/groff/pipeline.c
c++ -O  -o groff groff.o pipeline.o /usr/src/tools/groff/obj.i386/build/src/libs/libgroff/libgroff.a  -lm
groff.o: In function `main':
groff.o(.text+0x911): undefined reference to `__throw'
groff.o(.text+0x9d9): undefined reference to `__throw'
...

# c++ -v
Using builtin specs.
gcc version 2.95.3 20010315 (release) (NetBSD nb4)

Thoughts?

Cheers,

Patrick