Bug 1546870 - Make extracting .tar.xz work with mach artifact toolchain. r=froydnj

For some reason, using `tar -Jxf` with Windows paths fails, and that makes
`mach artifact toolchain` unable to pull .tar.xz archives on Windows.

However, executing `xz -d -c` works, and we can feed its output to
python's tarfile.

Differential Revision: https://phabricator.services.mozilla.com/D28779

--HG--
extra : moz-landing-system : lando

python/mozbuild/mozbuild/action/tooltool.py

@@ -559,7 +559,12 @@ def unpack_file(filename):
             return True
         clean_path(base_file)
         log.info('untarring "%s"' % filename)
-        if not execute('tar -Jxf %s 2>&1' % filename):
+        # Not using tar -Jxf because it fails on Windows for some reason.
+        process = Popen(['xz', '-d', '-c', filename], stdout=PIPE)
+        tar = tarfile.open(fileobj=process.stdout, mode='r|')
+        tar.extractall()
+        tar.close()
+        if not process.wait():
             return False
     elif zipfile.is_zipfile(filename):
         base_file = filename.replace('.zip', '')