This reduces the number of methods in the shader backend(the instr
modifiers can be handled in that wrapper) and it will help flow
control emulation in the ARB backend.

Once upon a time this was used for creating fake vertex shader
attribute semantics for d3d8 shaders. We don't need this anymore since
device_stream_info_from_declaration() will use the vertex
declaration's output slot to load the data, if present. That also
avoids the potentially expensive matching of attribute semantics
between vertex shader and declaration for d3d8.

Setting a NULL geometry shader doesn't hurt much, and it reduces console spam
a bit.

I.e., make sure that if a SM4 shader uses SV_POSITION it ends up as position
data.

SIZEOF looks just like one of the typical Win32 API capitalizations of
the basic C construct which it isn't.