Add missing native targets (#248)

Summary:
Depends on #247.

Ensure that `libextra` is included when building sonar targets. My
cleanup was a bit too aggressive.

Fixes #246
Pull Request resolved: https://github.com/facebook/flipper/pull/248

Reviewed By: jknoxville

Differential Revision: D9420724

Pulled By: passy

fbshipit-source-id: f2d0625507a4897051840c95feefc534583b080f

android/build.gradle

@@ -17,7 +17,7 @@ android {
         externalNativeBuild {
             cmake {
                 arguments '-DANDROID_TOOLCHAIN=clang', '-DANDROID_STL=c++_shared'
-                targets 'sonar'
+                targets 'sonar', 'event', 'event_extra', 'event_core'
             }
         }
     }