[libunwind] Fix SEH unwinding on ARM

Check `__SEH__` when checking if ARM EHABI should be implied,
similarly to 4a3722a2c3dff1fe885cc38bf43d3c095c9851e7 / D126866.

Fix a warning by using the right format specifier (PRIxPTR instead
of PRIx64), and add a double->float cast in a codepath that hasn't
been built so far.

This is enough to make SEH unwinding of itanium ABI exceptions on
ARM mostly work - one specific issue is fixed in a separate follow-up
patch.

Differential Revision: https://reviews.llvm.org/D126867

GitOrigin-RevId: 7c0e93cb89e6aa74881411213abf83faae7c58ee
4 files changed
tree: add31a8388ce554c22a29750345198a69f6565ef
  1. cmake/
  2. docs/
  3. include/
  4. src/
  5. test/
  6. .clang-format
  7. CMakeLists.txt
  8. LICENSE.TXT