[OpenMP] Fix build warnings

[sunshaoce]

Summary

llvm-project/openmp/libomptarget/src/private.h:260:9: warning: 'DEBUG_PREFIX' macro redefined [-Wmacro-redefined]
#define DEBUG_PREFIX GETNAME(TARGET_NAME)
        ^
llvm-project/openmp/libomptarget/include/ompt_device_callbacks.h:22:9: note: previous definition is here
#define DEBUG_PREFIX "OMPT"
        ^
1 warning generated.

llvm-project/openmp/libomptarget/plugins-nextgen/common/PluginInterface/PluginInterface.cpp:458:14: warning: moving a local object in a return statement prevents copy elision [-Wpessimizing-move]
      return std::move(Err);
             ^
llvm-project/openmp/libomptarget/plugins-nextgen/common/PluginInterface/PluginInterface.cpp:458:14: note: remove std::move call here
      return std::move(Err);
             ^~~~~~~~~~   ~
llvm-project/openmp/libomptarget/plugins-nextgen/common/PluginInterface/PluginInterface.cpp:552:12: warning: moving a local object in a return statement prevents copy elision [-Wpessimizing-move]
    return std::move(Err);
           ^
llvm-project/openmp/libomptarget/plugins-nextgen/common/PluginInterface/PluginInterface.cpp:552:12: note: remove std::move call here
    return std::move(Err);
           ^~~~~~~~~~   ~
2 warnings generated.

openmp/libomptarget/plugins-nextgen/common/PluginInterface/PluginInterface.cpp

if (MemoryManager)
     delete MemoryManager;
   MemoryManager = nullptr;
 
   if (RecordReplay.isRecordingOrReplaying())
     RecordReplay.deinit();
 
   if (RPCHandle)
     if (auto Err = RPCHandle->deinitDevice())
-      return std::move(Err);
+      return Err;
 
   return deinitImpl();
 }
 
 Expected<__tgt_target_table *>
 GenericDeviceTy::loadBinary(GenericPluginTy &Plugin,
                             const __tgt_device_image *InputTgtImage) {
   assert(InputTgtImage && "Expected non-null target image");
auto UsingOrErr =
       Server.isDeviceUsingRPC(*this, Plugin.getGlobalHandler(), Image);
   if (!UsingOrErr)
     return UsingOrErr.takeError();
 
   if (!UsingOrErr.get())
     return Plugin::success();
 
   if (auto Err = Server.initDevice(*this, Plugin.getGlobalHandler(), Image))
-    return std::move(Err);
+    return Err;
 
   auto DeviceOrErr = Server.getDevice(*this);
   if (!DeviceOrErr)
     return DeviceOrErr.takeError();
   RPCHandle = *DeviceOrErr;
   DP("Running an RPC server on device %d\n", getDeviceId());
   return Plugin::success();
 }

openmp/libomptarget/src/private.h

 };
 // Invalid GTID as defined by libomp; keep in sync
 #define KMP_GTID_DNE (-2)
 #ifdef __cplusplus
 }
 #endif
 
 #define TARGET_NAME Libomptarget
+#ifndef DEBUG_PREFIX
 #define DEBUG_PREFIX GETNAME(TARGET_NAME)
+#endif
 
 ////////////////////////////////////////////////////////////////////////////////
 /// dump a table of all the host-target pointer pairs on failure
 static inline void dumpTargetPointerMappings(const ident_t *Loc,
                                              DeviceTy &Device) {
   DeviceTy::HDTTMapAccessorTy HDTTMap =
       Device.HostDataToTargetMap.getExclusiveAccessor();
   if (HDTTMap->empty())