If it's ignored, a warning is printed to catch accidents, but not an
error since it should be possible to just append --info to existing
command line to see what the input is about.
Sigh, again. That's what I get for removing std::string only from some
APIs and not all. Explicitly fetching the argument values as a
StringView everywhere now, it avoids a copy so it's good to do even if
not strictly needed.
To make it convenient, the format equals to the usual file extension.
Currently skipping WGSL and DXIL however because I have no idea what
extension should they have, not even the DirectXShaderCompiler repo
tests show anything useful, there it's either generic LLVM *.ll or *.bc.
Come on, did people in 2020 also forget how to design file formats?!