misc: Replace M5_CLASS_VAR_USED with GEM5_CLASS_VAR_USED.

Change-Id: Ibd2230d684f41201b07fa9083881145e36176a68
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/45241
Tested-by: kokoro <noreply+kokoro@google.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>

src/mem/mem_interface.hh

@@ -140,7 +140,7 @@ class MemInterface : public AbstractMemory
     /**
      * General timing requirements
      */
-    M5_CLASS_VAR_USED const Tick tCK;
+    GEM5_CLASS_VAR_USED const Tick tCK;
     const Tick tCS;
     const Tick tBURST;
     const Tick tRTW;

src/mem/ruby/network/garnet/OutputUnit.hh

@@ -99,7 +99,7 @@ class OutputUnit : public Consumer
 
   private:
     Router *m_router;
-    M5_CLASS_VAR_USED int m_id;
+    GEM5_CLASS_VAR_USED int m_id;
     PortDirection m_direction;
     int m_vc_per_vnet;
     NetworkLink *m_out_link;