Add cargo-readelf subcommand.

[higuoxing]

Hi, I found that the cargo-readobj command proxies the llvm-readobj tool and uses --elf-output-style=GNU to make the output compatible with gnu-readelf. LLVM do provide a tool called llvm-readelf which is a symbolic link to llvm-readobj but is more compatible with gnu-readelf.

For example, gnu-readelf -s dumps symbols, llvm-readelf -s dumps symbols but llvm-readobj --elf-output-style -s dumps sections.

Do you have interest in adding cargo-readelf subcommand? I can give it a try.

[adamgreig]

I'd definitely like to see cargo-readelf here, especially if it's relatively simple to add and easy to maintain. It looks like rustup does not add a llvm-readelf to the toolchains dir, only llvm-readobj, but maybe we can invoke that in elf mode or something?