title: pass build_ext options to pip install
body: <p>Is there some way to pass <code>build_ext</code> options to pip install to alter how an extension included in a package is compiled? (Yes, I know that one can download the source and build/install with a custom <code>setup.cfg</code>, but I'm curious whether it is possible to pass options that can be specified in <code>setup.cfg</code> directly through pip.)</p>