It's obviously not the same, but you can emulate this with a conventional compiler:

  #if 0
  set -e; [ "$0" -nt "$0.bin" ] &&
  cc "$0" -o "$0.bin"
  exec "$0.bin" "$@"
  #endif
  
  #include <stdio.h>

  int
  main(int argc, char *argv[]) {
    puts("Hello world!");
    return 0;
  }

It works, because by default system shell will be spawned.

How does this work? Is there an alternate form for #! (aka shebang)?

EDIT: hah, I should have realized that "//" is the C comment and "//usr/bin/tcc" is equivalent to "/usr/bin/tcc". Clever!

I always love these things that are really scripts in two (or more) languages. Common is something like this on Windows to make a command script a Perl script. It lets you run your Perl script without having to make sure you had .pl extensions associated. Though, you needed Perl installed, so I never quite got the point.

    @rem = '--*--Perl-*--
    @echo off
    echo Hello from a command script
    perl -x -S %0 %*
    goto endofperl
    @rem ';
    #!perl
    print "Hello from Perl!\n";
    __END__
    :endofperl

By far very less common is to stuff some Perl code in a C# source file. A dev that was way too clever for his own code did this to have a Perl script that would update a C# script file and be self contained. This is a simple example of what it looked like, minus the instant headache anyone got that had to look at the real version:

    #if PerlScript
    $csharp=<<WhyJustWhy;
    #endif
    using System;

    namespace Example
    {
        public static class Program
        {
            static void Main()
            {
                Console.WriteLine("Hello from C#");
            }
        }
    }

    #if PerlScript
    WhyJustWhy
    print("Hello from Perl!")
    __END__
    #endif

"C comment," you mean.

So it's running the file as a shell script, where the first line runs tcc on the current file and quits.

Fixed typo, thanks. Yeah for some reason it didn't click when I saw it.

From man tcc(1):

    #!/usr/bin/tcc -run
    #include <stdio.h>
    
    int main()
    {
        printf("Hello World\n");
        return 0;
    }

D code can also be run this way:

    #!/usr/bin/rdmd
    void main() { import std.stdio; writeln("hello"); }

And add the -b commandline flag to enable the memory and bounds checker.

Just as a side note... It's important to say that it still does get compiled... it's not some kind of interpreted mode.