Add reboot binary if it exists to recovery

Change-Id: I7efdba5cf4addf0036ea04ab76a8ecc2c3456e2a
diff --git a/prebuilt/Android.mk b/prebuilt/Android.mk
index f1777c6..b5da5a9 100644
--- a/prebuilt/Android.mk
+++ b/prebuilt/Android.mk
@@ -98,6 +98,9 @@
     RELINK_SOURCE_FILES += $(TARGET_OUT_EXECUTABLES)/fsck.f2fs
     RELINK_SOURCE_FILES += $(TARGET_OUT_EXECUTABLES)/fibmap.f2fs
 endif
+ifneq ($(wildcard system/core/reboot/Android.mk),)
+    RELINK_SOURCE_FILES += $(TARGET_OUT_EXECUTABLES)/reboot
+endif
 
 TWRP_AUTOGEN := $(intermediates)/teamwin