Improve instruction emulation based stack unwinding on ARM

* Add and fix the emulation of several instruction.
* Disable frame pointer usage on Android.
* Specify return address register for the unwind plan instead of explict
  tracking the value of RA.
* Replace prologue detection heuristics (unreliable in several cases)
  with a logic to follow the branch instructions and restore the CFI
  value based on them. The target address for a branch should have the
  same CFI as the source address (if they are in the same function).
* Handle symbols in ELF files where the symbol size is not specified
  with calcualting their size based on the next symbol (already done
  in MachO files).
* Fix architecture in FuncUnwinders with filling up the inforamtion
  missing from the object file with the architecture of the target.
* Add code to read register wehn the value is set to "IsSame" as it
  meanse the value of a register in the parent frame is the same as the
  value in the current frame.

Differential revision: http://reviews.llvm.org/D10447

llvm-svn: 240533