Check for PLOG_DEFAULT_INSTANCE_ID instead of PLOG

include/rtc/global.hpp

@@ -39,7 +39,7 @@ enum class LogLevel { // Don't change, it must match plog severity
 typedef std::function<void(LogLevel level, string message)> LogCallback;
 
 RTC_CPP_EXPORT void InitLogger(LogLevel level, LogCallback callback = nullptr);
-#ifdef PLOG
+#ifdef PLOG_DEFAULT_INSTANCE_ID
 RTC_CPP_EXPORT void InitLogger(plog::Severity severity, plog::IAppender *appender = nullptr);
 #endif