add BUILD_NATIVE_BENCHMARK

Similar to BUILD_NATIVE_TEST, but links against libbenchmark
instead of libgtest.

Change-Id: I97d44db4807a79efa9bca56c108082ac45c943b8
diff --git a/core/config.mk b/core/config.mk
index 73acac9..d868e22 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -77,6 +77,7 @@
 BUILD_DROIDDOC:= $(BUILD_SYSTEM)/droiddoc.mk
 BUILD_COPY_HEADERS := $(BUILD_SYSTEM)/copy_headers.mk
 BUILD_NATIVE_TEST := $(BUILD_SYSTEM)/native_test.mk
+BUILD_NATIVE_BENCHMARK := $(BUILD_SYSTEM)/native_benchmark.mk
 BUILD_HOST_NATIVE_TEST := $(BUILD_SYSTEM)/host_native_test.mk
 BUILD_NOTICE_FILE := $(BUILD_SYSTEM)/notice_files.mk