Implement clGetICDLoaderInfoOCLICD.

[Kerilk]

This implements clGetICDLoaderInfoOCLICD as suggested in #182

With this change, clinfo reports:

ICD loader properties
  ICD loader Name                                 Khronos OpenCL ICD Loader
  ICD loader Vendor                               Khronos Group
  ICD loader Version                              3.0.4
  ICD loader Profile                              OpenCL 3.0

If we go ahead with this, the cl_icdl.h file should be moved to the header, and the cl_icdl extension should be properly defined.

I decided to keep the enumeration, rather than use defines as we usually do, because I am unsure of the side effects on big endian architectures. This will cause some headaches when defining the xml extension as I think no other enums are defined.

[Kerilk]

@bashbaug if we decide to merge this, rebasing #182 on this (or the other way around) should be straightforward.

[bashbaug]

Thanks for pulling this together - there are a lot of interesting ideas here!

[Kerilk]

GitHub action latest images seem to have been updated, and CI is breaking.

[Kerilk]

@MathiasMagnus any idea why the MacOS CI fails here:
https://github.com/KhronosGroup/OpenCL-ICD-Loader/actions/runs/3439072786
but not there:
https://github.com/Kerilk/OpenCL-ICD-Loader/actions/runs/3439072644

[bashbaug]

Thanks, all of my comments are resolved.

I think this needs a rebase now before merging.

Should we bump the rev number to 3.0.5?

[Kerilk]

@bashbaug I have rebased the code on main, and bumped version number to 3.0.5. Unless we want to do the header integration first, I think it is good to go.

[bashbaug]

Merging as agreed on the November 22 teleconference.