[lldb] Fix DW_OP_addrx uses.

Summary: DW_OP_GNU_addr_index has been renamed as DW_OP_addrx in the standard. clang produces DW_OP_addrx tags and with this change lldb starts to process them.

Reviewers: aprantl, jingham, davide, clayborg, serge-sans-paille

Reviewed By: aprantl

Subscribers: jdoerfert, dblaikie, labath, shafik, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D59004

llvm-svn: 355629