Extend unwind.h with the ARM unwinder interface.
Extend unwind.h with the ARM unwinder interface.

These declarations come from the sample code in the
"Exception Handling ABI for the ARM Architecture" document.


git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@148469 91177308-0d34-0410-b5e6-96231b3b80d8

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