The new structurizer therefore reaches feature parity with the
older simple one, except for a couple of points:
* the old structurizer accepts any CFG, without requiring reducibility;
however, the DXIL specification requires the CFG to be reducible
anyway, so we're not really losing anything;
* the new structurizer additionally requires that no block has two
incoming back arrows; AFAIK this is condition that can happen,
but in practice it seems to be rare; also, it's not hard to add
support for it, as soon as it is decided it is useful.
On the other hand, the new structurizer makes use of the merging
information that are reconstructed from the CFG, which is important
for downstream optimization and fundamental for correctly emitting
tangled instructions.
Taking these considerations into account, the old structurizer is
considered superseded and is therefore removed.
Properly passing the inverse-trig.shader_test tests whose qualifiers
have been removed requires making spirv.c capable of handling ABS.
The same happens for the ps_3_0 equality test in
float-comparison.shader_test.
