lldb needs to support DW_op_piece masks for values in subregister and also to be able to piece together a value that is spread across multiple registers.

Patch from Adrian Prantl.

<rdar://problem/16040521> 



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@212867 91177308-0d34-0410-b5e6-96231b3b80d8