[llvm][Docs] Add release notes about dwarf fission with relaxations (#169871)

Author: daniilavdeev

clang/docs/ReleaseNotes.rst

@@ -642,6 +642,9 @@ RISC-V Support
 - `__GCC_CONSTRUCTIVE_SIZE` and `__GCC_DESTRUCTIVE_SIZE` are changed to 64. These values are
   unstable according to `Clang's documentation <https://clang.llvm.org/docs/LanguageExtensions.html#gcc-destructive-size-and-gcc-constructive-size>`_.
 
+- DWARF fission is now compatible with linker relaxations, allowing `-gsplit-dwarf` and `-mrelax`
+  to be used together when building for the RISC-V platform.
+
 CUDA/HIP Language Changes
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 

llvm/docs/ReleaseNotes.md

@@ -149,6 +149,8 @@ Changes to the RISC-V Backend
 * Adds experimental support for the 'Zibi` (Branch with Immediate) extension.
 * Add support for Zvfofp8min (OFP8 conversion extension)
 * Adds assembler support for the Andes `XAndesvsinth` (Andes Vector Small Int Handling Extension).
+* DWARF fission is now compatible with linker relaxations, allowing `-gsplit-dwarf` and `-mrelax`
+  to be used together when building for the RISC-V platform.
 
 Changes to the WebAssembly Backend
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