PATCH: Support LD_AS_NEEDED

[Paul Brook]

> >> I don't recall any of those have caused any serious issues for
> >> linker debugging.
>
> > I've been bitten by LD_{RUN,LIBRARY}_PATH several times.
>
> Exactly. We know how to deal with them.

Let me rephrase: I've wasted too many hours (personally and with others) 
tracking down what ended up being a bogus LD_LIBRARY_PATH. i.e. I have 
empirical evidence of environment variables causing serious issues.

Paul