When a human reads code and then produces very similar code, that is infringement.
It is not, any more than when someone writes a book about elves, some Slashdotter parrots something they heard somewhere, or a half decent programmer writes any of the algorithms found in Numerical Methods. The GP is correct, copyright protects the specific expression, not the idea, and both law and precedent protect the case where you read something, put it down, then generate your own. Only substantial portions of exact text and distinctive and recognizable things like character names are protected, and even then only when there are no circumstances like a limited number of ways to write something.
Proving you did that can be tricky. THAT's why "clean-room" implementations were invented. You document the fact that the implementer had no contact with the original so any resulting expression is obviously not infringing.
GCC is covering their asses, as they should. They wrote a completely unenforceable policy so if some bit of code is found to infringe on something for whatever reason they can just remove it and blame the dastardly policy violating original submitter.