Work around `art-host-tests` build issues when using ART prebuilts.

Using prebuilts of the ART Module seems to make
`COMPATIBILITY.art-host-tests.HOST_SHARED_LIBRARY.FILES` empty on
x86 targets, thus breaking the `art-host-tests` build target. As
a workaround, relax the corresponding build rule to allow for an
empty `COMPATIBILITY.art-host-tests.HOST_SHARED_LIBRARY.FILES`
list.

Test: lunch cf_x86_phone-userdebug
        && SOONG_CONFIG_art_module_source_build=false m art-host-tests
Bug: 194627489
Change-Id: I9e885be3c7161f6f09a93b3d32339a5a6e57d2a1
diff --git a/core/tasks/art-host-tests.mk b/core/tasks/art-host-tests.mk
index d771b06..b9a349d 100644
--- a/core/tasks/art-host-tests.mk
+++ b/core/tasks/art-host-tests.mk
@@ -29,6 +29,7 @@
 $(art_host_tests_zip) : $(COMPATIBILITY.art-host-tests.FILES) $(my_host_shared_lib_for_art_host_tests) $(SOONG_ZIP)
 	echo $(sort $(COMPATIBILITY.art-host-tests.FILES)) | tr " " "\n" > $@.list
 	grep $(HOST_OUT_TESTCASES) $@.list > $@-host.list || true
+	$(hide) touch $@-host-libs.list
 	$(hide) for shared_lib in $(PRIVATE_HOST_SHARED_LIBS); do \
 	  echo $$shared_lib >> $@-host-libs.list; \
 	done