patch 8.1.0500: cleaning up in src/tee may not always work

Problem:    Cleaning up in src/tee may not always work.
Solution:   Use "rm" when appropriate. (Michael Soyka, closes #3571)

src/tee/Makefile

@@ -3,6 +3,12 @@
 CC=gcc
 CFLAGS=-O2 -fno-strength-reduce
 
+ifneq (sh.exe, $(SHELL))
+DEL = rm
+else
+DEL = del
+endif
+
 tee.exe: tee.o
 	$(CC) $(CFLAGS) -s -o $@ $<
 
@@ -10,6 +16,6 @@ tee.o: tee.c
 	$(CC) $(CFLAGS) -c $<
 
 clean:
-	- del tee.o
-	- del tee.exe
+	- $(DEL) tee.o
+	- $(DEL) tee.exe
 

src/version.c

@@ -792,6 +792,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    500,
 /**/
     499,
 /**/