Use order-only dependencies for symbols files

Use an order-only dependency from $(LOCAL_BUILT_MODULE) to the symbols
file so that wiping the symbols directory during installclean doesn't
force anything to rebuild.

Bug: 186507256
Test: m && rm -rf $OUT/symbols && m
Change-Id: Ic164819c71f9db6126ff91c58752c8727cde0d5e
diff --git a/core/dex_preopt_libart.mk b/core/dex_preopt_libart.mk
index 8f0702b..393053d 100644
--- a/core/dex_preopt_libart.mk
+++ b/core/dex_preopt_libart.mk
@@ -68,7 +68,7 @@
   endif
   LOCAL_MODULE_CLASS := ETC
   include $(BUILD_PREBUILT)
-  $(LOCAL_BUILT_MODULE): $(my_unstripped_installed)
+  $(LOCAL_BUILT_MODULE): | $(my_unstripped_installed)
   # Installing boot.art causes all boot image bits to be installed.
   # Keep this old behavior in case anyone still needs it.
   $(LOCAL_INSTALLED_MODULE): $(my_installed)