One problem:  Make is often using "if .defined(USE_NEW_TOOLCHAIN)"... so
how can you turn it off?  I would assume that USE_NEW_TOOLCHAIN=no will
still trip this.

Anyway:
/usr/src/gnu/lib/libgcc
# make
/usr/src/tool/bin/i386--netbsdelf-gcc -O2  -Werror -I/usr/src/gnu/lib/libgcc/../../usr.bin/gcc/arch/i386 -I/usr/src/gnu/lib/libgcc/../../dist/toolchain/gcc/cp/inc -DIN_GCC -DIN_LIBGCC2 -D__GCC_FLOAT_NOT_NEEDED -I/usr/src/gnu/lib/libgcc/../../dist/toolchain/gcc -I/usr/src/gnu/lib/libgcc/../../dist/toolchain/gcc/config -I/usr/src/gnu/lib/libgcc/../../dist/toolchain/gcc/../include -nostdinc -idirafter /usr/include -c -o exception.o /usr/src/gnu/lib/libgcc/../../dist/toolchain/gcc/cp/exception.cc /usr/src/gnu/lib/libgcc/../../dist/gcc/cp/exception.cc
i386--netbsdelf-gcc: cannot specify -o with -c or -S and multiple compilations
*** Error code 1
Why is exception.cc showing up twice?  We have a *VERY* twisty maze of
Makefiles these days; perhaps make needs debugging options to show how it
builds a command, and where the pieces come from?  I have searched around a
bit, and I can't find any rule that says "name two different versions of this
file".

-s