[android] add libatomic.a to linker in order solve link error when enable optimization
[android] add libatomic.a to linker in order solve link error when enable optimization

This will solve following error:
```
$ rake device
    Create ./build/Development-22/lib/armeabi/libpayload.so
/Users/watson/prj/RubyMotion/data/android/22/armv5te/librubymotion-static.a(ChildTarget.o):ChildTarget.cpp:function LLIChildTarget::handleExecute(): error: undefined reference to '__atomic_fetch_add_4'
/Users/watson/prj/RubyMotion/data/android/22/armv5te/librubymotion-static.a(ChildTarget.o):ChildTarget.cpp:function LLIChildTarget::handleExecute(): error: undefined reference to '__atomic_fetch_add_4'
/Users/watson/prj/RubyMotion/data/android/22/armv5te/librubymotion-static.a(ChildTarget.o):ChildTarget.cpp:function LLIChildTarget::handleExecute(): error: undefined reference to '__atomic_fetch_add_4'
/Users/watson/prj/RubyMotion/data/android/22/armv5te/librubymotion-static.a(ChildTarget.o):ChildTarget.cpp:function LLIChildTarget::handleExecute(): error: undefined reference to '__atomic_fetch_add_4'
clang++: error: linker command failed with exit code 1 (use -v to see invocation)
```

HipByte/RubyMotion,HipByte/RubyMotion,katsuyoshi/RubyMotion,hboon/RubyMotion,katsuyoshi/RubyMotion,katsuyoshi/RubyMotion,beni55/RubyMotion,hboon/RubyMotion,katsuyoshi/RubyMotion,HipByte/RubyMotion,beni55/RubyMotion,beni55/RubyMotion,hboon/RubyMotion,beni55/RubyMotion