Add cmake to source release tarballs

[kwk]

Summary

I've split the git archive generation into three steps:

1. generate pure tarball
2. append top-level cmake directory to all tarballs
3. compress the archive

This was inspired by D118252 and can be considered an alternative
approach for all projects to have access to the shared cmake
directory when building in standalone mode.

When generating source tarballs on my local laptop it takes 9 minutes and 45 seconds WITH this patch applied. When this patch is not applied, it takes 9minutes and 38 seconds. That means, this patch introduces a slowdown of 7 seconds, which seems fair.

[serge-sans-paille]

I like that approach. Have you tested that putting the shared cmakefile in that location is enough for individual project to honor them?

[kwk]

In D118481#3287759, @serge-sans-paille wrote:

I like that approach. Have you tested that putting the shared cmakefile in that location is enough for individual project to honor them?

Ups, no I could try that but so far I haven't. For current Fedora snapshots of LLVM I package the directory under a sub-package of llvm: llvm-cmake-devel. It installs the cmake files into a location that others can find: /usr/lib64/cmake/llvm.

The compiler-rt package is one consumer of this package and it seems to work.

[tstellar]

I think this is fine.

[kwk]

Rebased. No changes.

llvm/utils/release/export.sh

if [ -z "$snapshot" ]; then
         tar --sort=name --owner=0 --group=0 \
             --pax-option=exthdr.name=%d/PaxHeaders/%f,delete=atime,delete=ctime \
             -cJf test-suite-$release$rc.src.tar.xz test-suite-$release$rc.src
     fi
 
     for proj in $projects; do
         echo "Creating tarball for $proj ..."
         pushd $llvm_src_dir/$proj
-        git archive --prefix=$proj-$release$rc.src/ $tree_id . | xz >$target_dir/$(template_file $proj)
+        target_archive_file=$target_dir/$(template_file $proj)
+        trap "rm -fv $target_archive_file.tmp" EXIT
+        git archive --prefix=$proj-$release$rc.src/ -o $target_archive_file.tmp $tree_id .
+        # Get relative path to top-level cmake directory to be packaged
+        # alongside the project. Append that path to the tarball.
+        cmake_rel_path=$(realpath --relative-to=. $llvm_src_dir/cmake)
+        tar --append -f $target_archive_file.tmp $cmake_rel_path
+        cat $target_archive_file.tmp | xz > $target_archive_file
         popd
     done
 }
 
 while [ $# -gt 0 ]; do
     case $1 in
         -release | --release )
             shift