Introducing objcopy as a tool

[Edgar Fuß <ef%math.uni-bonn.de@localhost>]

When using a lang/gcc8 patched to use devel/binutils (because the base as 
chokes on what gcc generates), base strip/objcopy may be unable to cope with 
certain relocation types.

Now strip is easy because it is a tool, which can be redirected to use gstrip 
from the same pkgsrc binutils the compiler uses for as and ld.

But objcopy is not a tool.

Is there a recipie for adding a new tool? Or is there a better way to cope?