Add support for the ARM EHABI unwinder.

Only use the LLVM unwinder for ARM.

The LLVM unwinder now supports ARM EHABI, so we can finally use that for
exception handling on ARM. The unwinder doesn't work for other
architectures though (aside from on Darwin), so use libunwind for now.

Change-Id: Ife8b0b33dbfe96c10eab102cd36d30149d68ace9
2 files changed