Allow for SPIRV and binary support without OpenCL C

For our use case, we'd like to have OpenCL drivers that support SPIRV and binary input but optional OpenCL C support.
Apparently this might violate the spec as CL_DEVICE_COMPILER_AVAILABLE implies that SPIR-V support isn't available.
Some clarification needed here.

cc: @karolherbst

Read the OpenCL specification material covering SPIR-V, binary input, OpenCL C support, and CL_DEVICE_COMPILER_AVAILABLE. Compare those requirements with the use case in the issue and the existing three-comment discussion. Done means the specification’s intended behavior and any needed clarification are documented unambiguously.

Written by the indexing model from the issue text.