Sporadic error message rebuilding some ports: undefined reference to `copysignl'

[Yuri]

I see this message here and there. Once it came up during compile, I 
figured out that an extra gcc option '-lm' (explicitely adding libm) 
helps. Now devel/ddd fails in configure. But when I go into the 
directory and rerun configure with the same options by hand it succeeds.

Do you see such problem? What's the general fix?

Yuri