Fix compilation of boot image and oat

Change-Id: I7de0bb04adac4c68cb410cefec86f50bb30dddea
diff --git a/build/Android.oat.mk b/build/Android.oat.mk
index 57e5ce6..59bb771 100644
--- a/build/Android.oat.mk
+++ b/build/Android.oat.mk
@@ -69,4 +69,7 @@
 
 $(TARGET_BOOT_OAT): $(TARGET_BOOT_DEX) $(DEX2OAT_DEPENDENCY)
 	@echo "target dex2oat: $@ ($<)"
+	@mkdir -p $(dir $@)
 	$(hide) $(DEX2OAT) -Xms256m -Xmx256m $(addprefix --dex-file=,$(filter-out $(DEX2OAT),$^)) --oat=$@ --image=$(TARGET_BOOT_IMG) --base=$(IMG_TARGET_BASE_ADDRESS) --host-prefix=$(PRODUCT_OUT)
+
+$(TARGET_BOOT_IMG): $(TARGET_BOOT_OAT)