Yes that is an impressive list, but I bet if LLVM had gone with a license similar to GCC, and everything else remained equal, its adoption wouldn't be as it is.
No those projects aren't open source at all, they used their own compilers, or forked variants from GCC which you couldn't reveal thanks NDAs, now thanks to clang's license they have replaced their implementations, only contributing back what they feel relevant to open source.
No those projects aren't open source at all, they used their own compilers, or forked variants from GCC which you couldn't reveal thanks NDAs, now thanks to clang's license they have replaced their implementations, only contributing back what they feel relevant to open source.