macOS has llvm-otool in its CommandLineTools.
Is llvm-otool in llvm? I don't see it in the llvm source code at https://github.com/llvm-mirror/llvm.git.
Does anybody know where to find its source code?
Source code for open source parts of Apple software is available at https://opensource.apple.com/. Specifically, otool sources should be here: https://opensource.apple.com/source/cctools/ and here: https://opensource.apple.com/source/llvmCore/ (according to its man page, llvm-otool is just a shim that calls LLVM's objdump).