Update .debug_line parsing for DWARF 5

[philipc]

From the standard:
Replace the line number program header format with a new format that
provides the ability to use an MD5 hash to validate the source file version in
use, allows pooling of directory and file name strings and makes provision
for vendor-defined extensions. Also add a string section specific to the line
number table ( .debug_line_str ) to properly support the common practice
of stripping all DWARF sections except for line number information.