Bug 1728671: Use gettempdir() instead of tempdir r=firefox-build-system-reviewers,glandium

The `tempfile.tempdir` cache value isn't always populated, but
`tempfile.gettempdir()` always is. They both provide the same result.

Differential Revision: https://phabricator.services.mozilla.com/D124261

python/mozbuild/mozbuild/test/configure/common.py

@@ -41,7 +41,7 @@ class ConfigureTestVFS(object):
         self._paths = set(mozpath.abspath(p) for p in paths)
 
     def _real_file(self, path):
-        return mozpath.basedir(path, [topsrcdir, topobjdir, tempfile.tempdir])
+        return mozpath.basedir(path, [topsrcdir, topobjdir, tempfile.gettempdir()])
 
     def exists(self, path):
         if path in self._paths:

python/mozbuild/mozbuild/test/test_mozinfo.py

@@ -284,7 +284,7 @@ class TestWriteMozinfo(unittest.TestCase, Base):
                 MOZ_WIDGET_TOOLKIT="windows",
             )
         )
-        tempdir = tempfile.tempdir
+        tempdir = tempfile.gettempdir()
         c.topsrcdir = tempdir
         with NamedTemporaryFile(
             dir=os.path.normpath(c.topsrcdir), mode="wt"