[PATCH] Add IAS/EHABI changes to release notes

[Logan Chien]

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Comment at: docs/ReleaseNotes.rst:34

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I feel this paragraph can be made more clear with some reordering:

    After extensive testing and changes to cooperate with Dwarf unwinding,
    EHABI is enabled by default.  The options ``-arm-enable-ehabi``
    and ``-arm-enable-ehabi-descriptors``, which were used to enable
    EHABI in the previous releases, are removed now.


http://llvm-reviews.chandlerc.com/D3094