The hlsl_ir_compile node is introduced to represent the "compile"
syntax, and later the CompileShader() and ConstructGSWithSO()
constructs.
It basically represents a function call that remembers its arguments
using hlsl_srcs and keeps its own instruction block, which is discarded
when working on non-effect shaders.
For shader compilations it can be asserted that args_count is 1, and
that this argument (and the last node in hlsl_ir_effect_call.instrs)
is a regular hlsl_ir_call pointing to the declaration of the function
to be compiled.
This node type will be deleted once the hlsl->vsir->d3dbc translation is
complete. For now it serves the purpose of allowing to keep both real
hlsl_ir_nodes and vsir_instructions in the hlsl_block, until all the
former can be translated into the latter.
This is achieved by means of creating a variable storing zero,
loading every array element, comparing if the non-constant index
matches the index of that element at runtime, and in that case
store the corresponding element in the variable.
This seems to be the same strategy that the native compiler uses.
