building gcc 4.0 such that it implicitly knows where its header files are

[Noel Yap <noel.yap@xxxxxxxxx>]

What do I need to do to build gcc 4.0, such that when using it, it
knows where its own header files are.  IOW, such that the compile
implitly uses -I path/to/correct/system/header/files.

>From what I've read, that should be the default, but that's not the
behaviour I'm seeing.

Thanks,
Noel