[clang] [clang][doc][SYCL] Add SYCL driver and device library release notes to ReleaseNotes.md (PR #211949)

[Alexey Bader via cfe-commits]

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@@ -493,6 +493,32 @@ features cannot lower the translation-unit ABI level;
 
 #### Improvements
 
+- SYCL compilations now default to `-std=c++17` when no explicit language
+  standard is specified. Standards below C++17 are rejected with a diagnostic.
+
+- Clang now assumes the default target for SYCL device compilation is 64-bit
+  SPIR-V and diagnoses if a non-supporting target is specified on the command
+  line. (#GH167358)
+
+- The SYCL runtime shared library has been renamed from `libsycl.so` to
+  `libLLVMSYCL.so` to align with LLVM naming conventions.
+
+- SYCL header include paths are now added automatically for both host and
+  device compilations.
+
+- SYCL runtime library linking is now supported on Windows. When `-fsycl` is
+  specified, Clang automatically adds `/MD` if no explicit CRT flag is present,
+  links the appropriate debug (`LLVMSYCLd.lib`) or release (`LLVMSYCL.lib`)
+  library, and rejects static CRT flags (`/MT`, `/MTd`) with a diagnostic. Use
+  `-nolibsycl` to suppress automatic library linking.
+
+- Fixed `-nolibsycl` being silently ignored on Linux: the SYCL runtime library
+  was unconditionally added to the link line even when the flag was passed.
+
+- SYCL device compilations targeting SPIR-V now automatically link
+  `libclang_rt.builtins.bc` at compile time via `-mlink-builtin-bitcode`.
+  Pass `--no-offloadlib` to opt out.
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bader wrote:

I think the internal option is less important to the clang users than the functionality enabled by the library.

https://github.com/llvm/llvm-project/pull/211949