Update to D11825.

Summary:
Adding `-latomic` to `ANDROID_LINKER_FLAGS` doesn't actually work.
Adding `atomic` to `LLDB_SYSTEM_LIBS` does.

Related: D11831.

Reviewers: Andrzej, ovyalov

Subscribers: tberghammer, danalbert, srhines, lldb-commits

Differential Revision: http://reviews.llvm.org/D11840

llvm-svn: 244343