[gdb/testsuite] Require address update for DW_LNS_copy

No address update before a DW_LNS_copy might mean an incorrect dwarf
assembly test-case.

Try to catch such incorrect dwarf assembly test-cases by:
- requiring an explicit address update for each DW_LNS_copy, and
- handling the cases where an update is indeed not needed, by adding
  "DW_LNS_advance_pc 0".

Tested on aarch64-linux.