[LLD] Add ARM64EC release note (#116282)

Author: cjacek

lld/docs/ReleaseNotes.rst

@@ -43,6 +43,8 @@ COFF Improvements
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 * ``/includeglob`` has been implemented to match the behavior of ``--undefined-glob`` available for ELF.
 * ``/lldsavetemps`` allows saving select intermediate LTO compilation results (e.g. resolution, preopt, promote, internalize, import, opt, precodegen, prelink, combinedindex).
+* ``/machine:arm64ec`` support completed, enabling the linking of ARM64EC images.
+* COFF weak anti-dependency alias symbols are now supported.
 
 MinGW Improvements
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