And we have the right to blast them on Twitter for taking open source code and slapping their own license terms on it.
They however shouldn't break the law in the process. I am not a lawyer, but using gcc would require them to license products in GPL-compatible ways.
Using gcc doesn't make your work gpl.
Distributing GCC does.
In some sense, yes, using GCC puts limits on what you can legally do. The intent of those limits is well explained by Stallman. In case of API I highly suspect the intent is there. Now, how that intent is interpreted by reading GPL is another matter - though it would be sad to find a company abusing the legal system.
This is unenforceable and what it does is alienate the open source community built around Lattice, that, I may say, has only helped their sales. Very short sighted move of them.