-o is in the documentation, but not in the llvm-dwarfdump help text. This patch adds it by inverting the -o and --out-file aliasing. It also removes --out-file from the help text, since we don't really want people to be using this switch in practice.
I'm mildly against this change. IIRC, the idea was that --out-file is a long-form option that nobody uses in practice and we wanted people to prefer -o instead, which is what people are most familiar with working with compilers. So if -o shows up in the --help output, I'd leave it at that.
Just checked clang, and its documentation and help text both mention '-o' and not '--out-file' or another equivalent long-form. I'm happy to change this to expose the '-o' option and replace '--out-file' in the documentation with '-o', if you think that's wise? I don't think we want inconsistency between the help text and documentation.
(I'd be in favor of removing it, if it doesn't serve much purpose - does anyone know the history of why it was added?)
We've changed the behavior of llvm-dwarfdump pretty significantly over the years (these days it prints with coloured output, only dumping debug_info by default, and in non-verbose mode (skipping forms and other things)) - it's a fairly "compiler/debugger developer centric tool" which is a small enough audience we've been pretty comfortable making usability improvements even if they'd break some kind of compatibility.