[SEH] Implement filter capturing in CodeGen
While capturing filters aren't very common, we'd like to outline
__finally blocks in the frontend to simplify -O0 EH preparation and
reduce code size. Finally blocks are usually have captures, and this is
the first step towards that.
Currently we don't support capturing 'this' or VLAs.
Reviewers: majnemer
Differential Revision: http://reviews.llvm.org/D8825
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@234261
91177308-0d34-0410-b5e6-
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