rx: fix compilation for non-linux platforms

rx/src/SharedAtomic.cpp

@@ -200,6 +200,8 @@ int shared_atomic32::notify_n(int count) const {
       WakeByAddressSingle(const_cast<shared_atomic32 *>(this));
     }
   }
+
+  return 1; // FIXME
 }
 #else
 #error Unimplemented atomic for this platform

rx/src/SharedMutex.cpp

@@ -1,7 +1,5 @@
 #include "SharedMutex.hpp"
 #include "asm.hpp"
-#include <syscall.h>
-#include <unistd.h>
 
 namespace rx {
 void shared_mutex::impl_lock_shared(unsigned val) {