[OpenCL][5.0.0 Release] Release notes for OpenCL in Clang

[Anastasia]

Summary

Added release notes describing committed functionality for OpenCL in release 5.0.

[bader]

LGTM, except one nit.

docs/ReleaseNotes.rst

146

As far as I remember, this change was reverted as it had caused some regressions. I haven't fix them yet, so I users still have to explicitly specify void for empty parameter list.

[yaxunl]

LGTM. Thanks.

[Anastasia]

docs/ReleaseNotes.rst

146

Good spot. Thanks! I will remove this.

[Anastasia]

Removed description of reverted fuctionality.

[Anastasia]

Committed to release_50@311485

docs/ReleaseNotes.rst

 OpenCL C Language Changes in Clang
 ----------------------------------
 
-...
+Various bug fixes and improvements:
+-  Extended OpenCL-related Clang tests.
+-  Improved diagnostics across several areas: scoped address space
+   qualified variables, function pointers, atomics, type rank for overloading,
+   block captures, ``reserve_id_t``.
+-  Several address space related fixes for constant AS function scope variables,
+   IR generation, mangling of ``generic`` and alloca (post-fix from general Clang
+   refactoring of address spaces).
+-  Several improvements in extensions: fixed OpenCL version for ``cl_khr_mipmap_image``,
+   added missing ``cl_khr_3d_image_writes``.
+-  Improvements in ``enqueue_kernel``, especially the implementation of ``ndrange_t`` and blocks.
+-  OpenCL type related fixes: global samplers, the ``pipe_t`` size, internal type redefinition,
+   and type compatibility checking in ternary and other operations.
+-  The OpenCL header has been extended with missing extension guards, and direct mapping of ``as_type``
+   to ``__builtin_astype``.
+-  Fixed ``kernel_arg_type_qual`` and OpenCL/SPIR version in metadata.
+-  Added proper use of the kernel calling convention to various targets.
+
+The following new functionalities have been added:
+-  Added documentation on OpenCL to Clang user manual.
+-  Extended Clang builtins with required ``cl_khr_subgroups`` support.
+-  Add ``intel_reqd_sub_group_size`` attribute support.
+-  Added OpenCL types to ``CIndex``.
 
 OpenMP Support in Clang
 ----------------------------------