patch 8.1.1505: running "make clean" twice gives errors

Problem:    Running "make clean" twice gives errors.
Solution:   Add "-f" to "rm". (closes #4516)
diff --git a/src/testdir/Makefile b/src/testdir/Makefile
index bf64a03..d3c1184 100644
--- a/src/testdir/Makefile
+++ b/src/testdir/Makefile
@@ -85,9 +85,9 @@
 
 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
diff --git a/src/version.c b/src/version.c
index 82e9e38..13db304 100644
--- a/src/version.c
+++ b/src/version.c
@@ -778,6 +778,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1505,
+/**/
     1504,
 /**/
     1503,