Support to build with AAPT2

To build with AAPT2, set "USE_AAPT2=true".
TODO: Support split apks and generated resources from other than renderscript.

Bug: 25958912
Change-Id: I19b1a038824ce5b2a3d3ffadbce3173c845193fc
diff --git a/core/config.mk b/core/config.mk
index e5de5e9..7eb81ed 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -403,6 +403,7 @@
 ACP := $(HOST_OUT_EXECUTABLES)/acp
 AIDL := $(HOST_OUT_EXECUTABLES)/aidl
 AAPT := $(HOST_OUT_EXECUTABLES)/aapt
+AAPT2 := $(HOST_OUT_EXECUTABLES)/aapt2
 ZIPALIGN := $(HOST_OUT_EXECUTABLES)/zipalign
 SIGNAPK_JAR := $(HOST_OUT_JAVA_LIBRARIES)/signapk$(COMMON_JAVA_PACKAGE_SUFFIX)
 SIGNAPK_JNI_LIBRARY_PATH := $(HOST_OUT_SHARED_LIBRARIES)
@@ -422,6 +423,7 @@
 ACP := $(prebuilt_sdk_tools_bin)/acp
 AIDL := $(prebuilt_sdk_tools_bin)/aidl
 AAPT := $(prebuilt_sdk_tools_bin)/aapt
+AAPT2 := $(prebuilt_sdk_tools_bin)/aapt2
 ZIPALIGN := $(prebuilt_sdk_tools_bin)/zipalign
 SIGNAPK_JAR := $(prebuilt_sdk_tools)/lib/signapk$(COMMON_JAVA_PACKAGE_SUFFIX)
 # Use 64-bit libraries unconditionally because 32-bit JVMs are no longer supported