Move msvc specific define to msc toolset filter

Author: duckdoom5

build/Helpers.lua

@@ -107,7 +107,7 @@ function SetupNativeProject()
     defines { "DEBUG" }
 
   filter { "configurations:DebugOpt" }
-    defines { "DEBUG", "_ITERATOR_DEBUG_LEVEL=0" }
+    defines { "DEBUG" }
     optimize "Debug"
     runtime "Release"
 
@@ -117,6 +117,9 @@ function SetupNativeProject()
 
   -- Compiler-specific options
 
+  filter { "toolset:msc*", "configurations:DebugOpt" }
+    defines { "_ITERATOR_DEBUG_LEVEL=0" }
+
   filter { "toolset:msc*" }
     buildoptions { msvc_buildflags }
     defines { msvc_cpp_defines }