If SIP is kicking in, it sounds like you're using the clang that comes with Apple's developer tools. Does this same issue occur with clang sourced from homebrew, or from LLVM's own binary releases?
replyYes, it kicks in even with non apple supplied clang(most notably, with the clang supplied as part of the Android toolchain, since we sometimes build Android on MacOS and having to re-sign the google-supplied clang with our own certificate is now a regular thing every time there is an update released).
replyIf it's being sent to another developer then asking them to run xattr -rd com.apple.quarantine on the file so they can run it doesn't seem insurmountable. I agree that it's a non-starter to ask marketing or sales to do that, but developers can manage. Having to sign and then upload the binary to Apple to notarize is also annoying but you put it in a script and go about your day.
replyBut Apple being "completely open", it is not.