...FSF knew early on that all software hinges on having a freely available compiler. There's not much call for tweaking it, but I would note that practically every piece of free software out there does use GCC. Now, if GNU were to start clamping down on use of GCC libraries and the use of it for generating code under other licenses...

But then, everyone would just start forking off the current compiler which operates under the currently more liberal license. Which is more likely what will happen if business starts to get nervous with GPLv3. Just take the current snapshot of the software and tweak it to your hearts content. GNU can choose any license they want. But having licensed the software under terms less than GPLv3, they'll find that they're going to have a hard time getting followers.

As in all things, those who write the software get to determine what license they want to use. Those who consume the software get to decide whether they want to use the software. By all means, GNU has the right to put future versions under any license they wish. What they don't have the right to do is revoke the software that has been issued under past licenses. Nor do they have a right to automatically have producers and consumers of free software automatically fall in line.