replace unreachable returns by aborts

functionally identical but nicer, as discussed in PR

tensorflow/core/distributed_runtime/remote_device.cc

@@ -45,7 +45,7 @@ class RemoteDevice : public Device {
   ResourceMgr* resource_manager() override {
     LOG(FATAL) << "Accessing the resource manager of a remote device is not "
                << "supported.";
-    return nullptr;
+    std::abort();
   }
 
   bool IsLocal() const override { return false; }

tensorflow/core/framework/device_base.cc

@@ -70,7 +70,7 @@ const DeviceAttributes& DeviceBase::attributes() const {
 
 const string& DeviceBase::name() const {
   LOG(FATAL) << "Device does not implement name()";
-  return "";
+  std::abort();
 }
 
 void DeviceBase::set_eigen_cpu_device(Eigen::ThreadPoolDevice* d) {

tensorflow/core/platform/path.cc

@@ -328,7 +328,7 @@ string GetTempFilename(const string& extension) {
     }
   }
   LOG(FATAL) << "No temp directory found.";
-  return "";
+  std::abort();
 #endif
 }