runtime(indent-test): MS-Windows: Add Makefile for running indent tests

A few more unrelated changes:
- fix Vim script style of indent test
- Change comments to complete sentences in Filelist

closes: #14198
diff --git a/runtime/indent/Makefile b/runtime/indent/Makefile
index f6c4473..66ded80 100644
--- a/runtime/indent/Makefile
+++ b/runtime/indent/Makefile
@@ -1,5 +1,8 @@
 # Portable Makefile for running indent tests.
 
+.SUFFIXES:
+.PHONY: test clean testclean
+
 VIM = vim
 VIMRUNTIME = ..