Limit CMake targets to build

Summary:
This doesn't solve our build caching issue (GH230) but
helps a bit with build times as we can skip building all
sorts of test targets which are otherwise included.

The sonar target is the only thing we care about here.

Reviewed By: danielbuechele

Differential Revision: D9360117

fbshipit-source-id: 13a976243b48efbe0f69e9fe47780486f9688eb8

android/build.gradle

@@ -17,6 +17,7 @@ android {
         externalNativeBuild {
             cmake {
                 arguments '-DANDROID_TOOLCHAIN=clang', '-DANDROID_STL=c++_shared'
+                targets 'sonar'
             }
         }
     }