shader_signature_find_element_for_reg() is also used in the TPF parser,
where the program has not been validated yet, so it must not crash
on errors.
The I/O normaliser can instead assume that the shader is already
validated.
This fixes a crash with a shader used by The Falconeer. The bug is still
present, because the shader will be incorrectly rejected, but at least
the vkd3d-shader will fail gracefully.
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 way the same shader is always dumped to the same path and when
launching the same program over and over we avoid both creating new
copies of the same file each time and overwriting different dumped
shaders.
