Add implicit min-sdk if a test uses a main-dex list.

D8 is changing behavior so that passing main-dex related information is a
compile-time error if the minimum api level is not below native multi-dex
support.

Bug:
Test: ./art/test/testrunner/run_build_test_target.py art-gtest
Change-Id: If662d8bd33da8cb576b4a6af0e40c949125c36c0
diff --git a/build/Android.common_test.mk b/build/Android.common_test.mk
index d8014bd..be1791b 100644
--- a/build/Android.common_test.mk
+++ b/build/Android.common_test.mk
@@ -133,6 +133,7 @@
     LOCAL_MODULE_PATH := $(3)
     LOCAL_DEX_PREOPT_IMAGE_LOCATION := $(TARGET_CORE_IMG_OUT)
     ifneq ($(wildcard $(LOCAL_PATH)/$(2)/main.list),)
+      LOCAL_MIN_SDK_VERSION := 19
       LOCAL_DX_FLAGS := --multi-dex --main-dex-list=$(LOCAL_PATH)/$(2)/main.list --minimal-main-dex
     endif
     include $(BUILD_JAVA_LIBRARY)
@@ -148,6 +149,7 @@
     LOCAL_JAVA_LIBRARIES := $(HOST_TEST_CORE_JARS)
     LOCAL_DEX_PREOPT_IMAGE := $(HOST_CORE_IMG_LOCATION)
     ifneq ($(wildcard $(LOCAL_PATH)/$(2)/main.list),)
+      LOCAL_MIN_SDK_VERSION := 19
       LOCAL_DX_FLAGS := --multi-dex --main-dex-list=$(LOCAL_PATH)/$(2)/main.list --minimal-main-dex
     endif
     include $(BUILD_HOST_DALVIK_JAVA_LIBRARY)