[1/18] d3dx9: Add shader assembler private definitions

[Juan Lang]

> The assembler requires quite some code to be at least minimally
> working (i.e. to implement a somewhat working D3DXAssembleShader
> function).

Is it not possible to implement enough to support some small subset of
the language?  If it's not at all possible, then we'll just have to
live with it.. but the odds of a favorable review get rather long.  So
if it would be possible to support the simplest shader program you can
think of with some subset of the code, that would be a worthwhile
approach, in my opinion.

Cheers,
--Juan