[DWARF v5] Add limited support for dumping .debug_rnglists

This change adds support to llvm-dwarfdump for dumping DWARF5
.debug_rnglists sections in regular ELF files.

It is not complete, in that several DW_RLE_* encodings are currently
not supported, but does dump the headert and the basic ranges for
DW_RLE_start_length and DW_RLE_start_end encodings.

Obvious next steps are to add verbose dumping that dumps the raw
encodings, rather than the interpreted contents, to add -verify support
of the section (e.g. to show that the correct number of offsets are
specified), add dumping of .debug_rnglists.dwo, and to add support for
other encodings.

Reviewed by: dblaikie, JDevlieghere

Differential Revision: https://reviews.llvm.org/D42481

llvm-svn: 324077