Earlier quoted context omitted.
Open source and Free software are essentially equivalent when it comes to licensing. The difference is in their motivation. So when RMS says that, he's saying Clang/LLVM opened up the source code in order help their software perform better and see wider usage. Whereas RMS's goal for GCC is to ensure freedom for its users. Technical superiority is great, but it is not the goal, and may be sacrificed if necessary to ac…
There's a couple claims here: 1) Free means freedom in the copyleft sense. 2) Free means freedom in the open source sense. 3) Free means free as in beer. In the article RMS appears to be using definition 1, elsewhere on the FSF site the FSF uses 2. "In the free software movement, we campaign for the freedom of the users of computing. The values of free software are fundamentally different from the values of open sour…
It is possible to be both unfree, and support dictatorships, like the USSR. RMS's goal with GCC, is to be like the mythical free country that also supports freedom and discourages dictatorships elsewhere in the world.
In other words, your software can be free, and yet support and aid those who would take your freedom away. This is the claim RMS is making of Clang.