Double floating point precision is an extension of OpenCL, which might
not be implemented by certain drivers, such as Intel Xe graphics.
Cycles does not use double floating point precision, and there is no
need on keeping doubles unless there is an explicit decision to use
them.
This is a simple fix from Cycles side to replace double floating point
type with a type of same size and alignment rules. Inspired by Brecht
and Patrick.
Tested on NVidia Titan V, Radeon RX Vega M, and TGL laptop.
Differential Revision: https://developer.blender.org/D10143
226eb5e366