patch 8.0.0178: command count test fails on MS-Windows

Problem:    test_command_count may fail when a previous test interferes, seen
            on MS-Windows.
Solution:   Run it separately.
diff --git a/src/testdir/Make_all.mak b/src/testdir/Make_all.mak
index 63a1b05..956d321 100644
--- a/src/testdir/Make_all.mak
+++ b/src/testdir/Make_all.mak
@@ -144,6 +144,7 @@
 	    test_channel.res \
 	    test_charsearch.res \
 	    test_cmdline.res \
+	    test_command_count.res \
 	    test_crypt.res \
 	    test_cscope.res \
 	    test_diffmode.res \