patch 8.1.1505: running "make clean" twice gives errors

Problem:    Running "make clean" twice gives errors.
Solution:   Add "-f" to "rm". (closes #4516)

Author: brammool

src/testdir/Makefile

@@ -85,9 +85,9 @@ RUN_VIM = VIMRUNTIME=$(SCRIPTSOURCE); export VIMRUNTIME; $(VALGRIND) $(VIMPROG)
 
 clean:
 	-rm -rf *.out *.failed *.res *.rej *.orig
-	-rm opt_test.vim test.log test_result.log messages
-	-rm $(RM_ON_RUN) $(RM_ON_START)
-	-rm valgrind.*
+	-rm -f opt_test.vim test.log test_result.log messages
+	-rm -f $(RM_ON_RUN) $(RM_ON_START)
+	-rm -f valgrind.*
 
 test1.out: test1.in
 	-rm -rf $*.failed $(RM_ON_RUN) $(RM_ON_START) wrongtermsize

src/version.c

@@ -777,6 +777,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1505,
 /**/
     1504,
 /**/