devel/qbs: mark BROKEN

(The build system) qbs fails to build when QScript is built with
clang13 and any kind of optimization. There's an upstream bug
for this,
https://bugreports.qt.io/browse/QBS-1684
but no resolution yet. Since QScript is -- maybe not *deprecated*,
but not-really-maintained -- unlikely to get fixes, we end up
with qbs blocking its one single consumer, qtcreator. But qtcreator
doesn't actually need qbs and can get by without.

So mark as broken, so that the package builders will stop complaining.