Hi,

you can replace the entire "configure" phase.

Search for "replace 'configure" in gnu/packages/*.scm .

You can find the entire block when you search for "--enable-fast-install" comments in gnu/packages/*.scm .

It is:

  (arguments
   `(#:phases
       (modify-phases %standard-phases
         (replace 'configure
           (lambda* (#:key inputs outputs (configure-flags '()) #:allow-other-keys)
             (apply invoke
                    `("./configure"
                      ,(string-append "--prefix=" out)
                      ,(string-append "--sysconfdir=/etc")
                      ,@configure-flags))))))