Enforcing struct layout

OpenCL C doesn't provide a guarantee for the struct layout particularly alignment aren't specified (which is implementation-defined in C99) therefore making it difficult to exchange data between host and device. Is this something that can be reasonably enforced?

Start by reviewing the OpenCL C struct layout and alignment material in the OpenCL-Docs sources, focusing on the stated host-to-device data exchange problem. Determine whether the specification can define a portable layout guarantee and identify the affected specification sections; done means a concrete, reviewable scope for any proposed clarification or change.

Written by the indexing model from the issue text.