Rebaseline llvm-libunwind tree

[am11]

The purpose of this PR is to extract all the changes we have on top of upstream/original copy: https://github.com/llvm/llvm-project/tree/llvmorg-9.0.0/libunwind in a separate commit. This will make it possible bring llvm-libunwind to the same plan as other external dependencies trees under src/native/external directory in a followup PR.

Please merge it without squashing the commits, otherwise it will defeat its purpose.

• first commit deletes the directory

• second commit extracts the upstream version:

  # bash on Ubuntu
  $ pushd src/coreclr/nativeaot
  $ curl -sSL https://github.com/llvm/llvm-project/archive/llvmorg-9.0.0.tar.gz |\
  tar xzf - llvm-project-llvmorg-9.0.0/libunwind --strip-components=1
  $ popd

• third commit is a copy over of current version of src/coreclr/nativeaot/libunwind, which contain all the changes transipred since the initial bringup in Use LLVM libunwind for stack unwinding on Unix corert#2293. It includes commits listed in:

  • https://github.com/dotnet/corert/commits/2dfab60ad1c3d0fe0241b5e2503fb3f8d33e4c22/src/Native/libunwind
  • https://github.com/dotnet/runtimelab/commits/9a766d3ae49e332bdc6c6545f5d2f02570cf97e2/src/coreclr/src/nativeaot/libunwind
  • https://github.com/dotnet/runtimelab/commits/9a766d3ae49e332bdc6c6545f5d2f02570cf97e2/src/coreclr/nativeaot/libunwind
  • https://github.com/dotnet/runtime/commits/aafa91036e1efd3d4dcb67eeb261cb6d8f774685/src/coreclr/nativeaot/libunwind

I have listed all those commits in description of third commit.

Contributes to #72344

[MichalStrehovsky]

Thank you!

[jkotas]

cc @VSadov

@am11 Should this be merged as rebase and merge ?

[am11]

@am11 Should this be merged as rebase and merge ?

Yes please. We just need a reference to the third commit from main branch, for bookkeeping additional modifications in version file. In next PR, I'll move this directory under src\native\external and add the version file.

[VSadov]

@am11 - very nice! Thanks!

BTW, #71187 has some libunwind fixes, but I think the llvm-libunwind already has similar fixes, so it may not have any impact here.

[VSadov]

rebase and merge is "Not enabled for this branch". I assume someone has the necessary permissions?