add include guards to GLDebug.h

src/GLDebug.h

@@ -2,13 +2,18 @@
 // NOTE: get useful debug messages from opengl
 // 	https://www.khronos.org/opengl/wiki/Debug_Output
 
+#ifndef GL_DEBUG_H
+#define GL_DEBUG_H
+
 #include <GL/glew.h>
 
 #include "shader.h"
 
 
 void dumpShader(GLuint prog_id);
+
 const char* glEnumToString(GLenum e);
+
 void openglDebugCallback(GLenum source,
 	GLenum type,
 	GLuint id,
@@ -17,6 +22,8 @@ void openglDebugCallback(GLenum source,
 	const GLchar* message,
 	const void* userParam);
 
+#endif // GL_DEBUG_H
+
 
 #ifdef GL_DEBUG_IMPLEMENTATION