[lld] Fix typo in 15.x release notes

The flag is -femit-dwarf-unwind, not -femit-compact-unwind.

Author: smeenai

lld/docs/ReleaseNotes.rst

@@ -98,7 +98,7 @@ MachO Improvements
 
 * We now support proper relocation and pruning of EH frames. **Note:** this
   comes at some performance overhead on x86_64 builds, and we recommend adding
-  the ``-femit-compact-unwind=no-compact-unwind`` compile flag to avoid it.
+  the ``-femit-dwarf-unwind=no-compact-unwind`` compile flag to avoid it.
   (`D129540 <https://reviews.llvm.org/D129540>`_,
   `D122258 <https://reviews.llvm.org/D122258>`_)