This deprecates the use of release-build LLVM hosted by the LLVM project, which makes debugging harder for developers. This PR implements the following solution: 1. Create LLVM release tarballs with assert enabled on our own (using Docker) 2. Host them in our own GitHub repositories 3. Use our LLVM for CI and/or development if `TRITON_USE_ASSERT_ENABLED_LLVM=1` is set.