bpo-30207: Install the Lib/test/support directory. (#1369)

diff --git a/Makefile.pre.in b/Makefile.pre.in
index 2b054684..57ee092 100644
--- a/Makefile.pre.in
+++ b/Makefile.pre.in
@@ -1044,6 +1044,7 @@
 		test/data test/cjkencodings test/decimaltestdata test/xmltestdata \
 		test/imghdrdata \
 		test/subprocessdata \
+		test/support \
 		test/tracedmodules \
 		encodings compiler hotshot \
 		email email/mime email/test email/test/data \