The use of c++0x should be limited to the small AtomicPointer class in port_posix.h. The class uses <cstdatomic> for its implementation. If you can provide a different implementation of "acquire store" and "release load" for your architecture, you should be all set without the need for c++0x.
I suspect that you may find suitable code in the chromium source code. See leveldb's port_chromium.h.
I suspect that you may find suitable code in the chromium source code. See leveldb's port_chromium.h.