fix C++17 error when working with sorting the structs

Index: AI/Skirmish/BARb/src/circuit/module/EconomyManager.cpp
--- AI/Skirmish/BARb/src/circuit/module/EconomyManager.cpp.orig
+++ AI/Skirmish/BARb/src/circuit/module/EconomyManager.cpp
@@ -553,7 +553,9 @@ void CEconomyManager::Init()
 				? (mspInfoEnd.pull - mspInfoBegin.pull) / (mspInfoEnd.mex - mspInfoBegin.mex)
 				: 0.f;
 	}
-	std::sort(mspInfos.begin(), mspInfos.end());
+	std::sort(mspInfos.begin(), mspInfos.end(), [](const circuit::CEconomyManager::SPullMtoS &a1, const circuit::CEconomyManager::SPullMtoS &a2){
+		return a1.mex < a2.mex;
+	});
 	pullMtoS = mspInfos.front().pull;
 
 	CSetupManager::StartFunc subinit = [this](const AIFloat3& pos) {
