Add conditional compiler define for MSVC compiler.

Fix #1845 [skip travis]

Source/Urho3D/CMakeLists.txt

@@ -204,7 +204,7 @@ endif ()
 
 # Generate platform specific export header file
 if (MSVC)
-    set (PRE_EXPORT_HEADER "\n#pragma warning(disable: 4251)\n#pragma warning(disable: 4275)\n")
+    set (PRE_EXPORT_HEADER "\n#pragma warning(disable: 4251)\n#pragma warning(disable: 4275)\n\n#if _MSC_VER < 1900\n#define strtoll _strtoi64\n#define strtoull _strtoui64\n#endif\n\n")
 endif ()
 if (URHO3D_CLANG_TOOLS)
     set (ANNOTATE_NONSCRIPTABLE "__attribute__((annotate(\"nonscriptable\")))")