Added GLFW_INCLUDE_NONE.

README.md

@@ -136,6 +136,8 @@ header instead of the regular OpenGL header.
 `GLFW_INCLUDE_ES3` makes the header include the OpenGL ES 3.0 `GLES3/gl3.h`
 header instead of the regular OpenGL header.
 
+`GLFW_INCLUDE_NONE` makes the header not include any client API header.
+
 `GLFW_INCLUDE_GLU` makes the header include the GLU header.  This only makes
 sense if you are using OpenGL.
 
@@ -286,6 +288,8 @@ GLFW.
    instead of `GL/gl.h`
  * Added `GLFW_INCLUDE_ES2` macro for telling the GLFW header to use
    `GLES2/gl2.h` instead of `GL/gl.h`
+ * Added `GLFW_INCLUDE_NONE` macro for telling the GLFW header to not include
+   any client API header
  * Added `GLFW_VISIBLE` window hint and parameter for controlling and polling
    window visibility
  * Added `GLFW_REPEAT` key action for repeated keys

include/GL/glfw3.h

@@ -172,7 +172,7 @@ extern "C" {
 #if defined(__APPLE_CC__)
   #if defined(GLFW_INCLUDE_GLCOREARB)
     #include <OpenGL/gl3.h>
-  #else
+  #elif !defined(GLFW_INCLUDE_NONE)
     #define GL_GLEXT_LEGACY
     #include <OpenGL/gl.h>
   #endif
@@ -188,7 +188,7 @@ extern "C" {
     #include <GLES2/gl2.h>
   #elif defined(GLFW_INCLUDE_ES3)
     #include <GLES3/gl3.h>
-  #else
+  #elif !defined(GLFW_INCLUDE_NONE)
     #include <GL/gl.h>
   #endif
   #if defined(GLFW_INCLUDE_GLU)