Emit DW_LLE_base_address + DW_LLE_offset_pair for DWARF v5

This patch tries to reduce the size of the debug_loclist section by
replacing the DW_LLE_start_length opcodes currently emitted by dsymutil
in favor of using DW_LLE_base_address + DW_LLE_offset_pair instead.

The DW_LLE_start_length is one AddressSize followed by a ULEB per entry,
whereas, the DW_LLE_base_address + DW_LLE_offset_pair will use one
AddressSize for the base address, and then the DW_LLE_offset_pair is a
pair of ULEBs. This will be more efficient where a loclist fragment has
many entries.

Differential Revision: https://reviews.llvm.org/D153080