[PATCH] configure: Add sanity checking for environment variables

[David Bremner]

David Bremner <david at tethera.net> writes:

> Passing in environment variables incompatible with the compiler may
> cause other parts of the configure script to fail in hard to
> understand ways, so we abort early.
> ---
> Gah, I left out the one line I actually wanted feedback on.

pushed to master, amended s/  minimal.c/ minimal.c/