Check build type consistency.

src/glow/glow.hh

 #pragma once
 
+#ifdef _DEBUG
+#ifndef GLOW_DEBUG
+#error Visual Studio is set to debug but CMake is not. Settings must match.
+#endif
+#else
+#ifdef GLOW_DEBUG
+#error CMake is set to debug but Visual Studio is not. Settings must match.
+#endif
+#endif
+
 namespace glow
 {
 /// OpenGL Version information