Use demangle for function names.

Bug: 62141808

Test: Ran unit tests, ran debuggerd -b on android processes.
Change-Id: I40f341bcb2b35dd0a020d245d6b6f2ed2df65481
diff --git a/libbacktrace/Android.bp b/libbacktrace/Android.bp
index 7dd9227..a643a29 100644
--- a/libbacktrace/Android.bp
+++ b/libbacktrace/Android.bp
@@ -113,6 +113,7 @@
             static_libs: ["libasync_safe", "libcutils"],
         },
     },
+    whole_static_libs: ["libdemangle"],
 }
 
 cc_library_shared {