Swift-5.2: on non-ubuntu linux build symlinks trouble

  1. fix recursive symlinks :

    rm -rdf llbuild/include/llvm/Demangle/include
    rm -rdf llbuild/lib/llvm/Demangle/include
    mkdir -p llbuild/lib/llvm/Demangle/include/llvm
    ln -s ../../../../../include/llvm/Demangle llbuild/lib/llvm/Demangle/include/llvm/Demangle

  2. fix missing dir build/buildbot_linux/swiftpm-linux-x86_64/x86_64-pc-linux-gnu/release :

ln -s ../x86_64-unknown-linux-gnu/release build/buildbot_linux/swiftpm-linux-x86_64/x86_64-pc-linux-gnu/

Yeah, I've seen that first one, don't know about second.

I think the reason of second problem - on discrepancies in platform detection...

x86_64-unknown-linux-gnu