Adds support for hardware watchpoints on Arm targets.

http://reviews.llvm.org/D9703

This updated patches correct problems in arm hardware watchpoint support patch posted earlier.

This patch has been tested on samsung chromebook (ARM - Linux) and PandaBoard using basic watchpoint test application.

Also it was tested on Nexus 7 Android device.

On chromebook linux we are able to set and clear all types of watchpoints but on android we end up getting a watchpoint packet error because we are not able to call hardware watchpoint ptrace functions successfully.

llvm-svn: 245961