Fix arm EHABI code to work. armhf had exception test failing without EHABI support.
No known upstream bug about this. Actual code change is more like workaround than
something that upstream would accept. Proper fix would be adding _Unwind_Control_Block
to clang unwind.h. _Unwind_Control_Block should also extend _Unwind_Exception to make
sure their ABI stays in sync.
No known upstream bug about this.
Gbp-Pq: Topic libcxx
Gbp-Pq: Name libcxxabi-arm-ehabi-fix.patch