[DebugInfo] Allow parsing line tables aligned to 4 or 8-byte boundaries

This allows the DWARFDebugLine::SectionParser to try parsing line tables
at 4 or 8-byte boundaries if the unaligned offset appears invalid. If
aligning the offset does not reduce errors the offset is used unchanged.

This is needed for llvm-dwarfdump to be able to extract the line tables
(with --debug-lines) from binaries produced by certain compilers that
like to align each line table in the .debug_line section. Note that this
alignment does not seem to be invalid since the units do point to the
correct line table offsets via the DW_AT_stmt_list attribute.

Differential Revision: https://reviews.llvm.org/D143513