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/Make_mvc.mak b/runtime/indent/Make_mvc.mak
index 0f73d7f..a50494d 100644
--- a/runtime/indent/Make_mvc.mak
+++ b/runtime/indent/Make_mvc.mak
@@ -4,7 +4,7 @@
 
 .SUFFIXES:
 
-VIM = vim.exe
+VIMPROG = vim.exe
 VIMRUNTIME = ..
 
 # Run the tests that didn't run yet or failed previously.
@@ -12,7 +12,7 @@
 # If a test fails a testdir\*.fail file will be written.
 test :
 	@ set "VIMRUNTIME=$(VIMRUNTIME)"
-	$(VIM) --clean --not-a-term -u testdir\runtest.vim
+	$(VIMPROG) --clean --not-a-term -u testdir\runtest.vim
 
 
 clean testclean :