Integrate dexpreopt into the build system.

Change-Id: Id67f85d0f5c8674f5bc22e431114ca73625811ef
diff --git a/core/config.mk b/core/config.mk
index 897af83..a3bcbf1 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -215,6 +215,8 @@
 JARJAR := $(HOST_OUT_JAVA_LIBRARIES)/jarjar.jar
 PROGUARD := external/proguard/bin/proguard.sh
 JAVATAGS := build/tools/java-event-log-tags.py
+DEXOPT := $(HOST_OUT_EXECUTABLES)/dexopt$(HOST_EXECUTABLE_SUFFIX)
+DEXPREOPT := dalvik/tools/dex-preopt
 
 # ACP is always for the build OS, not for the host OS
 ACP := $(BUILD_OUT_EXECUTABLES)/acp$(BUILD_EXECUTABLE_SUFFIX)