patch 9.0.0560: elapsed time since testing started is not visible

Problem:    Elapsed time since testing started is not visible.
Solution:   Show the elapsed time while running tests.
diff --git a/src/testdir/Make_ming.mak b/src/testdir/Make_ming.mak
index 0638ade..2676111 100644
--- a/src/testdir/Make_ming.mak
+++ b/src/testdir/Make_ming.mak
@@ -47,6 +47,7 @@
 	@if exist test.log ( copy /y test.log test_result.log > nul ) \
 		else ( echo No failures reported > test_result.log )
 	$(VIMPROG) -u NONE $(COMMON_ARGS) -S summarize.vim messages
+	-if exist starttime del starttime
 	@echo.
 	@echo Test results:
 	@cmd /c type test_result.log
@@ -60,6 +61,7 @@
 	-if exist $@.res del $@.res
 	-if exist test.log del test.log
 	-if exist messages del messages
+	-if exist starttime del starttime
 	@$(MAKE) -f Make_ming.mak $@.res VIMPROG=$(VIMPROG) --no-print-directory
 	@type messages
 	@if exist test.log exit 1
@@ -83,6 +85,7 @@
 	-@if exist test.log $(DEL) test.log
 	-@if exist test_result.log del test_result.log
 	-@if exist messages $(DEL) messages
+	-@if exist starttime $(DEL) starttime
 	-@if exist benchmark.out del benchmark.out
 	-@if exist opt_test.vim $(DEL) opt_test.vim
 	-@if exist guidialog $(DEL) guidialog
@@ -92,6 +95,7 @@
 	-@if exist test.log $(DEL) test.log
 	-@if exist test_result.log del test_result.log
 	-@if exist messages $(DEL) messages
+	-@if exist starttime $(DEL) starttime
 
 
 # Tiny tests.  Works even without the +eval feature.