Be more careful about symlinking a file that actually exists on the host.

Avoids this error on later runs:

  ln: cannot create symbolic link from '/sys/kernel/debug' to 'out/target/product/walleye/root/d/debug': Permission denied

Bug: http://b/145148158
Test: touch * ; mm -j32 -k
Change-Id: I0c1c0c6e7666c0bc3373687d8c1c7bdf0847913f
diff --git a/rootdir/Android.mk b/rootdir/Android.mk
index 994d9ae..002c690 100644
--- a/rootdir/Android.mk
+++ b/rootdir/Android.mk
@@ -76,7 +76,7 @@
     ln -sf /system/bin $(TARGET_ROOT_OUT)/bin; \
     ln -sf /system/etc $(TARGET_ROOT_OUT)/etc; \
     ln -sf /data/user_de/0/com.android.shell/files/bugreports $(TARGET_ROOT_OUT)/bugreports; \
-    ln -sf /sys/kernel/debug $(TARGET_ROOT_OUT)/d; \
+    ln -sfn /sys/kernel/debug $(TARGET_ROOT_OUT)/d; \
     ln -sf /storage/self/primary $(TARGET_ROOT_OUT)/sdcard
 ifdef BOARD_USES_VENDORIMAGE
   LOCAL_POST_INSTALL_CMD += ; mkdir -p $(TARGET_ROOT_OUT)/vendor