misc: Replace M5_VAR_USED with GEM5_VAR_USED.

Change-Id: I64a874ccd1a9ac0541dfa01971d7d620a98c9d32
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/45231
Tested-by: kokoro <noreply+kokoro@google.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>

src/base/loader/elf_object.cc

@@ -141,7 +141,7 @@ ElfObject::ElfObject(ImageFileDataPtr ifd) : ObjectFile(ifd)
             "No loadable segments in '%s'. ELF file corrupted?\n",
             imageData->filename());
 
-    for (M5_VAR_USED auto &seg: image.segments())
+    for (GEM5_VAR_USED auto &seg: image.segments())
         DPRINTFR(Loader, "%s\n", seg);
 
     // We will actually read the sections when we need to load them

src/base/remote_gdb.cc

@@ -441,7 +441,7 @@ BaseRemoteGDB::detach()
 void
 BaseRemoteGDB::addThreadContext(ThreadContext *_tc)
 {
-    M5_VAR_USED auto it_success = threads.insert({_tc->contextId(), _tc});
+    GEM5_VAR_USED auto it_success = threads.insert({_tc->contextId(), _tc});
     assert(it_success.second);
     // If no ThreadContext is current selected, select this one.
     if (!tc)

src/base/stats/group.cc

@@ -67,7 +67,7 @@ Group::regStats()
 
     for (auto &g : statGroups) {
         if (Debug::Stats) {
-            M5_VAR_USED const SimObject *so =
+            GEM5_VAR_USED const SimObject *so =
                 dynamic_cast<const SimObject *>(this);
             DPRINTF(Stats, "%s: regStats in group %s\n",
                     so ? so->name() : "?",

src/base/vnc/vncserver.cc

@@ -376,7 +376,7 @@ VncServer::checkProtocolVersion()
 {
     assert(curState == WaitForProtocolVersion);
 
-    M5_VAR_USED size_t len;
+    GEM5_VAR_USED size_t len;
     char version_string[13];
 
     // Null terminate the message so it's easier to work with