Before this patch, we could only link against the back-deployment libc++abi
dylib. This patch allows linking against the just-built libc++abi, but
running against the back-deployment one -- just like we do for libc++.
Also, add XFAIL markup to flag expected errors.
Differential Revision: https://reviews.llvm.org/D91069
Added __cxxabi_config.h includes to resolve _LIBCXXABI_ARM_EHABI and
proper building the forces_unwindX.cpp tests for the ARM/EHABI targets.
Differential Revision: https://reviews.llvm.org/D96378
libunwind ARM EHABI does not support _Unwind_ForcedUnwind yet.
In addition, ARM EHABI makes `_Unwind_Exception` a typedef so
`struct _Unwind_Exception*` cannot be used.
Forced unwinding is like a foreign exception, which can be caught by `catch (...)` and rethrown.
If not rethrown, `__cxa_end_cath` will call `_Unwind_DeleteException` to destroy the object.
The behavior going through empty `throw()` and non-empty `throw(int)` is not
clear (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98785), so I do not add such
tests.
Differential Revision: https://reviews.llvm.org/D95200
Louis Dionne