ART: Enable multilib compilation for libartpalette

Fixes Android boot for Mac host builds.

Test: Full Android build on mac, check library exists in product.
Change-Id: I1fb9eaca0862770eadcf00f27c007d7788185ae3
diff --git a/libartpalette/Android.bp b/libartpalette/Android.bp
index 778109d..3e7354b 100644
--- a/libartpalette/Android.bp
+++ b/libartpalette/Android.bp
@@ -26,7 +26,7 @@
 art_cc_library {
     name: "libartpalette-system",
     defaults: ["libartpalette_defaults"],
-
+    compile_multilib: "both",
     target: {
         android: {
           srcs: ["system/palette_android.cc",],