Math: missing include for std::max() on MSVC.

Enabled only for MSVC, as GCC/Clang has max() in some (way smaller)
internal header and that is preferred to keep compilation times in sane
bounds.

src/Magnum/Math/Vector.h

@@ -30,6 +30,9 @@
  */
 
 #include <cmath>
+#ifdef _MSC_VER
+#include <algorithm> /* std::max() */
+#endif
 #include <Corrade/Utility/Assert.h>
 #include <Corrade/Utility/ConfigurationValue.h>
 #include <Corrade/Utility/Debug.h>