The versions of Clang and LLVM that you have today will ALWAYS be available under the license they're currently under.
You're fear-mongering that the current contributors of Clang and LLVM may, in the future, make new releases under licenses you don't like.
But if people like Clang and LLVM, they can fork the current code, and keep adding features to it under a compatible FOSS license.
This is a bold claim! Are you providing the hosting?
The versions of Clang and LLVM that you have today will ALWAYS be available under the license they're currently under.
You're fear-mongering that the current contributors of Clang and LLVM may, in the future, make new releases under licenses you don't like.
But if people like Clang and LLVM, they can fork the current code, and keep adding features to it under a compatible FOSS license.