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

[dinama]

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/

[Finagolfin]

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

[dinama]

@Finagolfin

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