[BOLT][DWARF] Fix handling of loclists_base without location accesses

There are CUs that have DW_AT_loclists_base, but no DW_AT_location in children
DIEs. Pre-bolt it points to a valid offset. We were not updating it, so it ended
up pointing in the middle of a list and caused LLDB to print out errors. Changed
it to point to first location list. I don't think it should matter since there
are no accesses to it anyway.

Reviewed By: maksfb

Differential Revision: https://reviews.llvm.org/D149798