speedo: Add new option STATIC=1

This can be used to build GnuPG with static versions of the core
gnupg libraries. For example:

make -f build-aux/speedo.mk STATIC=1 SELFCHECK=0 \

INSTALL_PREFIX=/somewhere/gnupg22  native

The SELFCHECK=0 is only needed to build from a non-released version.
You don't need it with a released tarball.

• Signed-off-by: Werner Koch <wk@gnupg.org>