[release] Use threaded compression with xz

Use xz -T0 to use your threads

Reviewed By: tstellar

Differential Revision: https://reviews.llvm.org/D131470

llvm/utils/release/export.sh

@@ -112,7 +112,7 @@ export_sources() {
     echo "$rc" > $target_dir/llvm-rc-$yyyymmdd.txt
     echo "$git_rev" > $target_dir/llvm-git-revision-$yyyymmdd.txt
 
-    git archive --prefix=llvm-project-$release$rc.src/ $tree_id . | xz >$target_dir/$(template_file llvm-project)
+    git archive --prefix=llvm-project-$release$rc.src/ $tree_id . | xz -T0 >$target_dir/$(template_file llvm-project)
     popd
 
     if [ -z "$snapshot" ]; then
@@ -131,7 +131,7 @@ export_sources() {
     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 $proj)
+        git archive --prefix=$proj-$release$rc.src/ $tree_id . | xz -T0 >$target_dir/$(template_file $proj)
         popd
     done
 }