You've always been able to use gcc to compile non-gpl code into an executable, and distribute it.
You've always been able to distribute a distro that includes gcc and also includes gpl-incompatible programs (like flash player, or apache-licensed programs).
What has to be GPL is the application that you combine the gcc code with, either when you link in the new libgccjit, or in your python code that imports the python module that links to libgccjit, or if you modify/extend the code for gcc itself (or other GPL codebases).
Can a GPL-licensed interpreter run non-GPL scripts? It seems like one should be able to build a GPL JIT+interpreter as a single application, then run whatever scripts they want on top of it.
The GPL applies to "derivative works", which is a legal term without a precise technical definition.
If you decide to write an interpreter for an existing language, and run existing programs on it, then those existing programs "probably" do not have to be under the GPL, for definitions of "probably" that Legal will not be happy about.
If you write an interpreter for a made-up language and then write programs in that language as part of a thinly-veiled scheme to do an end-run around the GPL, then that "probably" violates the GPL.
There is currently no bright-line rule separating those cases; this is something IP lawyers argue about themselves and reach wildly different conclusions.
