You can only sort of do that with gcc/clang. The #if 0 trick relies on funny behavior that is in a few common shells. When you try to execve(2) a script without a proper #! shebang, the kernel will return ENOEXEC. Bash will check for ENOEXEC then check a few heuristics to see if it looks like a text file, and if it does, then it will try to run it as a shell script.

This means that your script will work when run from a shell, but won't work when exec()ed from a non-shell program, which is a weird foot-gun.