[MC] Use unique_ptr to manage WinFrameInfos, NFC

[MC] Use unique_ptr to manage WinFrameInfos, NFC

The FrameInfo cannot be stored directly in the vector because chained
frames may refer to parent frames, so we need pointers that are stable
across a vector resize.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@315080 91177308-0d34-0410-b5e6-96231b3b80d8