toplevel Makefile gcc questions

[DJ Delorie]

> "install-no-fixedincludes" is for binaries which don't want the fixed
> includes.

This is for preparing a binary distribution, where you want to install
everything except the headers.

> "install-cross" is for cross builds, so that you can silently lose all
> languages except C and C++ (huh?).

I'm not sure about this one.

> "install.all" is used, uh, by, no, that wouldn't work... it still seems
> redundant with "install".

I suspect that configure could redirect "install" to default to
different targets.  This is one of them.