patch 8.0.1179: Test_popup_and_window_resize() does not always pass

Problem:    Test_popup_and_window_resize() does not always pass.
Solution:   Do not use $VIMPROG, pass the Vim executable in the vimcmd file.
            (Ozaki Kiichi, closes #2186)
diff --git a/src/testdir/Makefile b/src/testdir/Makefile
index ce1c24c..3a69c6c 100644
--- a/src/testdir/Makefile
+++ b/src/testdir/Makefile
@@ -126,18 +126,21 @@
 newtestssilent: $(NEW_TESTS)
 
 
-.vim.res:
-	@echo "$(RUN_VIMTEST)" > vimcmd
+.vim.res: writevimcmd
+	@echo "$(VIMPROG)" > vimcmd
+	@echo "$(RUN_VIMTEST)" >> vimcmd
 	$(RUN_VIMTEST) $(NO_INITS) -S runtest.vim $*.vim
 	@rm vimcmd
 
 test_gui.res: test_gui.vim
-	@echo "$(RUN_GVIMTEST)" > vimcmd
+	@echo "$(VIMPROG)" > vimcmd
+	@echo "$(RUN_GVIMTEST)" >> vimcmd
 	$(RUN_VIMTEST) -u NONE $(NO_INITS) -S runtest.vim $<
 	@rm vimcmd
 
 test_gui_init.res: test_gui_init.vim
-	@echo "$(RUN_GVIMTEST_WITH_GVIMRC)" > vimcmd
+	@echo "$(VIMPROG)" > vimcmd
+	@echo "$(RUN_GVIMTEST_WITH_GVIMRC)" >> vimcmd
 	$(RUN_VIMTEST) -u gui_preinit.vim -U gui_init.vim $(NO_PLUGINS) -S runtest.vim $<
 	@rm vimcmd