Based on the design document, "The runtime will not clamp or validate
the input, but implementations may clamp to the range [0,1] if necessary.",
so we test for the EXT_depth_range_unrestricted extension, and only clamp if
it's not available (thus, necessary to do so).
NaNs are converted to zero as per "NaNs must be treated as 0, but the runtime
will convert NaNs to 0 on behalf of the implementation.", and a default bounds
are set to 0.0 and 1.0.
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.
