Upstream NextPNR has moved to disable the GUI by default; it tends to
cause the most complications/bug reports and has various complexities
and failure modes (e.g. I've still had problems getting it working
efficiently on my Ice Lake laptop.)
Instead, disable GUI support by default, and add a new `nextpnrWithGui`
derivation that enables it. This cuts the closure size down by 40ish
percent (~800MB -> ~500MB) and makes it a neglibile amount faster.
It also fixes two bugs:
1) We were using the old `ICEBOX_ROOT` parameter for ice40 support,
now known as `ICESTORM_ICE40_PREFIX`, and
2) the CMake option `SERIALIZE_CHIPDB` was renamed to `..._CHIPDBS`
(with an 'S' suffix) which should speed up the build at the cost
of RAM usage
Signed-off-by: Austin Seipp <aseipp@pobox.com>
3dbe656a25