<rdar://problem/13477795>

crashlog.py was always subtracting 1 to point to the previous instruction when symbolicating ARM backtraces. Many times the backtraces will include bit zero set to 1 to indicate thumb, so we need to make sure we mask the address and then backup one for non frame zero frames.



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@178812 91177308-0d34-0410-b5e6-96231b3b80d8