g++ -print-prefix or -print-install-prefix

[Benjamin Kosnik]

> Why do you need this?  For installed-compiler testing, the compiler 
> already searches the obvious places.  (I'm not trying to be cute: I'm 
> genuinely curious.)

This is needed if you need to find the C++ includes, but are not using
the C++ compiler.

> I agree that it would be nice if -print-search-dirs listed include 
> directories.  It already lists the paths searched for programs and 
> libraries, so that seems like a logical place to add header directories.

Yep. Mostly, I was just curious: it seemed like an omission.

-benjamin