patch 9.1.0527: inconsistent parameter in Makefiles for Vim executable

Problem:  inconsistent parameter in Makefiles for Vim executable
Solution: consistently use $VIMPROG across all Makefiles
          (RestorerZ)

closes: #15099

Signed-off-by: RestorerZ <restorer@mail2k.ru>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/indent/Makefile b/runtime/indent/Makefile
index 66ded80..36a3f15 100644
--- a/runtime/indent/Makefile
+++ b/runtime/indent/Makefile
@@ -3,14 +3,14 @@
 .SUFFIXES:
 .PHONY: test clean testclean
 
-VIM = vim
+VIMPROG = vim
 VIMRUNTIME = ..
 
 # Run the tests that didn't run yet or failed previously.
 # If a test succeeds a testdir/*.out file will be written.
 # If a test fails a testdir/*.fail file will be written.
 test:
-	VIMRUNTIME=$(VIMRUNTIME) $(VIM) --clean --not-a-term -u testdir/runtest.vim
+	VIMRUNTIME=$(VIMRUNTIME) $(VIMPROG) --clean --not-a-term -u testdir/runtest.vim
 
 
 clean testclean: