scripts: set default CFLAGS to optimise.

The extra CFLAGS override the product defaults, causing the product to
be built without optimisation or debug. Be explicit and add these in.

Reported-by: Johannes Stezenbach <js@sig21.net>
Signed-off-by: Michael Hope <michael.hope@linaro.org>
Message-Id: <CANLjY-=3Gbio6nzUPhhevDHV7cUN=6Vigooe9nSf-RnGCqnjog@mail.gmail.com>
Patchwork-Id: 198808

 #!/bin/sh

 set -e

 printf "Running autoconf...\n"

 autoconf -Wall --force

 printf "Done. You may now run:\n    ./configure\n"