Allocating local mem in device functions is not explictly forbidden by the SPIR-V OpenCL Env

Currently it's possible to create a SPIR-V that allocates local mem in non-kernel functions although this is explicitly forbidden in OpenCL C spec for obvious implementation challenges. It is even accepted by various drivers (which likely just inline everything anyhow, effectively making the allocation happen inside the kernel).

Shall we add a check to the SPIR-V OpenCL Env for this case?

Start by reviewing the SPIR-V OpenCL Env specification and the OpenCL C restriction on local memory allocation in non-kernel functions. Determine where environment validity rules are defined; done means the environment explicitly forbids this allocation case and the relevant specification text is updated.

Written by the indexing model from the issue text.