The cmath "fix" was not needed after all, the includes order decides.

Global.h

@@ -58,6 +58,8 @@ static_assert(sizeof(bool) == 1, "Bool needs to be 1 byte in size.");
 /* Commonly used C++, Boost headers */
 /* ---------------------------------------------------------------------------- */
 #define WIN32_LEAN_AND_MEAN		// Exclude rarely-used stuff from Windows headers
+#define _USE_MATH_DEFINES
+
 #include <cstdio>
 #include <stdio.h>
 

client/battle/CBattleInterface.cpp

@@ -34,12 +34,7 @@
 #include "../gui/CGuiHandler.h"
 #include "../CMT.h"
 
-#if defined(_MSC_VER) && _MSC_VER >= 1800
-#define _USE_MATH_DEFINES
-#include <cmath>
-#else
-const double M_PI = 3.14159265358979323846;
-#endif
+
 #include "../../lib/UnlockGuard.h"
 
 using namespace boost::assign;