Fix several issues around .ARM.exidx section handling

* Use .ARM.exidx as a fallback unwind plan for non-call site when the
  instruction emulation based unwind failed.
* Work around an old compiler issue where the compiler isn't sort the
  entries in .ARM.exidx based on their address.
* Fix unwind info parsing when the virtual file address >= 0x80000000
* Fix bug in unwind info parsing when neither lr nor pc is explicitly
  restored.

Differential revision: http://reviews.llvm.org/D13380

llvm-svn: 249119