Bug#1020802: libz3-4: Xorg crashes on startup due to illegal instruction (SSE2) in libz3-4

[karogyoker999]

> As far as I see your MR just adds a dependency to sse2-support,
> which I guess just makes the installation abort in case of a CPU
> not supporting sse2, so I guess this would just make
> mesa not installable on your hardware?

Exactly.

It will abort the installation as it wouldn't work anyways.
Mesa now requires SSE2 and therefore Xorg as well.
The workaround is to use Wayland with GNOME or KDE.
But KDE requires SSE2 since several months too (and therefore fails to install).
It is better to have the installation fail rather than
having an unusable system after install. Because in the latter case,
it would mean that users would be disappointed, much time would be wasted
to troubleshoot. Failing the installation with a clear error message
is a much better solution.

The alternative would be to disable SSE2 for all i386 packages of libz3-4.
But usually maintainers don't like that since that would have a performance
impact on Pentium 4 CPUs. So there is a choice to make: disable SSE2 on
all x86_32 CPUs or fail the install on everything except Pentium 4.

There is a Debian patch [1] for the z3 package which does something with SSE2.
But then why is it still crashing? Maybe z3 has some hardcoded SSE2
instruction somewhere?
Or it has been just compiled with the incorrect compiler flags?

To have both performance and compatibility, a runtime check would be needed
to be added, but that would mean a significant amount of work.

Until this work is not done by someone, failing the installation is
still better than
crashing and leaving the system in an unbootable state.

[1]: https://sources.debian.org/patches/z3/4.8.12-1/00-intrinsics.patch/