[AArch64][libunwind] Unwinding support for return address signing with B Key

- Support for the case where the return address has been signed with the B key
- When the B key is used, a 'B' character is present in the augmentation string
  of CIE associated with the FDE for the function.

Differential Revision: https://reviews.llvm.org/D55704



git-svn-id: https://llvm.org/svn/llvm-project/libunwind/trunk@349339 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed