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/src/Make_mvc.mak b/src/Make_mvc.mak
index 511bfe8..adcf19a 100644
--- a/src/Make_mvc.mak
+++ b/src/Make_mvc.mak
@@ -1435,7 +1435,7 @@
 
 testgvim testgui:
 	cd testdir
-	$(MAKE) /NOLOGO -f Make_mvc.mak VIMPROG=..\gvim
+	$(MAKE) /NOLOGO -f Make_mvc.mak "VIMPROG=..\gvim.exe"
 	cd ..
 
 testtiny:
@@ -1445,7 +1445,7 @@
 
 testgvimtiny:
 	cd testdir
-	$(MAKE) /NOLOGO -f Make_mvc.mak tiny VIMPROG=..\gvim
+	$(MAKE) /NOLOGO -f Make_mvc.mak "VIMPROG=..\gvim.exe" tiny
 	cd ..
 
 testclean: