base-stats: Fix self addition bug in addStatGroup

A group cannot be added to itself; otherwise, it would
create a cyclic dependency.

Change-Id: I2e42f84814c675e8d5318cfda2d99b1b394758aa
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/43011
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Maintainer: Giacomo Travaglini <giacomo.travaglini@arm.com>

src/base/stats/group.cc

@@ -113,6 +113,7 @@ Group::addStat(statistics::Info *info)
 void
 Group::addStatGroup(const char *name, Group *block)
 {
+    panic_if(block == this, "Stat group can't be added to itself");
     panic_if(statGroups.find(name) != statGroups.end(),
              "Stats of the same group share the same name `%s`.\n", name);