libunwind is added to the static depedencies

libunwindbacktrace no longer includes libunwind. So, libunwind is
explicitly added to the dependency list.

Bug: 64730695
Test: build 2017 pixel device
Test: m dex2oats
Change-Id: Id2e987bbe17483aa9bea47b4da2f5ae4e6244713
diff --git a/Android.bp b/Android.bp
index 1b66e6f..569179d 100644
--- a/Android.bp
+++ b/Android.bp
@@ -11,6 +11,7 @@
     "libbacktrace",
     "libcutils",
     "libunwindbacktrace",
+    "libunwind",
     "libutils",
     "libbase",
     "liblz4",