Turn on LTO for libc++.so

For arm64-userdebug, binary size increased from 725KB to 748KB (3.1%).

Test: presubmit
Change-Id: I0277dbe93ee20e91619d255d71fcd75933faa24c

Android.bp

@@ -172,6 +172,9 @@ cc_library_shared {
     whole_static_libs: ["libc++_static"],
     stl: "none",
 
+    lto: {
+        thin: true,
+    },
     afdo: true,
 
     target: {