crash_reporter: add missing mkdir for crash_server rule

When doing a clean build, creating this file fails because the dir does
not yet exist:
echo "" > out/target/product/brilloemulator_arm/obj/ETC/crash_server_intermediates/crash_server
/bin/bash: out/target/product/brilloemulator_arm/obj/ETC/crash_server_intermediates/crash_server: No such file or directory

Bug: 24989289
Change-Id: If204dc0eb32e95ee66f97b568b4b9ae4050d3591
diff --git a/crash_reporter/Android.mk b/crash_reporter/Android.mk
index 11dfcbc..5dd9418 100644
--- a/crash_reporter/Android.mk
+++ b/crash_reporter/Android.mk
@@ -106,6 +106,7 @@
 # will log it as a configuration error.
 $(LOCAL_BUILT_MODULE): BRILLO_CRASH_SERVER ?= ""
 $(LOCAL_BUILT_MODULE):
+	$(hide)mkdir -p $(dir $@)
 	echo $(BRILLO_CRASH_SERVER) > $@
 endif