Peter Colberg

The second commit in https://github.com/intel/llvm/pull/5896 stacks on top of https://github.com/intel/llvm/pull/5895. I will drop the first commit in https://github.com/intel/llvm/pull/5896 once https://github.com/intel/llvm/pull/5895 is merged.

@tyoungsc I copied the changes to the specification and the implementation verbatim from your commit e1619fa64616a05ae962952b7bc6517af9f74dda, but noticed that the type of `min_capacity` is `size_t` in the specification while it...

> > Needless to say, the spec and the implementation should agree. I see that you also use `size_t` for the `map` and `unmap` member functions of the host pipe...

The SPIRV API uses `int32_t` for data type size, alignment, and `min_capacity`, see [`ConstantPipeStorage`](https://github.com/intel/llvm/blob/bc0579a56f7f4beee209ff58e4cf6e6e401e9876/sycl/include/CL/__spirv/spirv_types.hpp#L151-L157) and [`__spirv_ReadPipe`/`__spirv_WritePipe`](https://github.com/intel/llvm/blob/bc0579a56f7f4beee209ff58e4cf6e6e401e9876/sycl/include/CL/__spirv/spirv_ops.hpp#L733-L740). So really the question is whether `int32_t` should be exposed to the user or...