DWARF: Compensate for compiler's off-by-one instruction.

The compiler generates stackmaps with PC value which is *after*
the instruction rather PC of the instruction itself. This causes
trouble when generating native line number mapping since the
branch instruction itself will not be mapped, and consequently
we get incorrect line number in backtraces. Add code to compensate
for this. See the in-code comment for more details.

Change-Id: I72c992e6d08a767f314290d562421b251ae60732