Building old systems

[Brook Milligan]

I am trying to build an old kernel with build.sh on a recent (9.99.108) amd64 
system.  However, compiling nbmake fails immediately with errors like

        /usr/bin/ld: buf.o:(.bss+0x0): multiple definition of `debug_file'; 
arch.o:(.bss+0x0): first defined here 

Unless I am doing something silly, it clearly is not possible for a current 
system to build old tools and kernels at arbitrary points in time.

What is the best strategy for building old kernels to, for example, bisect the 
code?

Cheers,
Brook