[scudo] Condition variable can be disabled by setting the flag to off (#77532)

To enable the condition variable, you have to define both
UseConditionVariable and the ConditionVariableT. Otherwise, it'll be
disabled. However, you may want to disable the condition variable by
setting UseConditionVariable=false, for example, while measuring the
performance and you want to turn it off temporarily. Instead of
requiring the removal of the variable, examining its value makes more
sense.

Author: ChiaHungDuan

compiler-rt/lib/scudo/standalone/condition_variable.h

@@ -51,7 +51,7 @@ struct ConditionVariableState {
 
 template <typename Config>
 struct ConditionVariableState<Config, decltype(Config::UseConditionVariable)> {
-  static constexpr bool enabled() { return true; }
+  static constexpr bool enabled() { return Config::UseConditionVariable; }
   using ConditionVariableT = typename Config::ConditionVariableT;
 };