[clang] [clang][SYCL] Add SYCL spelling for AS attributes (PR #200849)

[Tom Honermann via cfe-commits]

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@@ -3603,6 +3597,9 @@ def err_attribute_address_multiple_qualifiers : Error<
 def warn_attribute_address_multiple_identical_qualifiers : Warning<
   "multiple identical address spaces specified for type">,
   InGroup<DuplicateDeclSpecifier>;
+def warn_deprecated_sycl_constant : Warning<
+  "'sycl_constant' address space attribute is deprecated">,
+  InGroup<DeprecatedAttributes>;
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tahonermann wrote:

I think we should not issue a deprecation warning for use of this attribute. The reason being that these attributes are intended for implementation of the SYCL library; not for use by SYCL programmers. From a SYCL specification perspective, what is deprecated is `sycl::access::address_space::constant_space`, sycl::constant_ptr`, and the related `sycl::multi_ptr` specializations and it is uses of those that should prompt a deprecation warning.

https://github.com/llvm/llvm-project/pull/200849