Add header that declares atomic primitives

It fixes a compilation issue:

/fdevent/fdevent_poll.cpp -o core/adb/fdevent/fdevent_poll.cpp.o
In file included from core/adb/fdevent/fdevent_poll.cpp:20:
In file included from core/adb/fdevent/fdevent_poll.h:29:
core/adb/fdevent/fdevent.h:106:10: error: no template named 'atomic' in namespace 'std'
    std::atomic<bool> terminate_loop_ = false;
    ~~~~~^

Change-Id: I5305a69a50e2638f514c5a7d47a9612b8ee38c69