Fix darwin build

Darwin needs libbase too.

Test: 'm'
Change-Id: I9d50face92b7d5a4399dbcebd39d4062477b3a2c
diff --git a/libbacktrace/Android.bp b/libbacktrace/Android.bp
index 10a4e46..be56531 100644
--- a/libbacktrace/Android.bp
+++ b/libbacktrace/Android.bp
@@ -83,6 +83,9 @@
     target: {
         darwin: {
             enabled: true,
+            shared_libs: [
+               "libbase",
+             ],
         },
         linux: {
             srcs: libbacktrace_sources,