gcc seems to be a funny stub that generates an "executable" that prints "Hello, World!" if the input file fuzzy-matches a hello world, and otherwise prints nothing.

Seems to be a few simple regexes: to "compile" you need a "main(" with either int or void before, and to trigger the hello world behavior you need printf( and a "hello" inside quotes. But that seems to be it:

  void main(
  //printf(" hello"