Add support for GLFW_NATIVE_INCLUDE_NONE macro

By default, the glfw3native.h header will include the platform-specific
headers necessary for the return types of GLFW native access functions.

Sometimes it is preferrable to declare those types

This commit adds support for the GLFW_NATIVE_INCLUDE_NONE macro, which
when defined disables the inclusion of all platform-specific headers.

Fixes #1348

README.md

@@ -146,6 +146,7 @@ information on what to include when reporting a bug.
    values to select ANGLE backend (#1380)
  - Added `GLFW_X11_XCB_VULKAN_SURFACE` init hint for selecting X11 Vulkan
    surface extension (#1793)
+ - Added `GLFW_NATIVE_INCLUDE_NONE` for disabling inclusion of native headers (#1348)
  - Added `GLFW_BUILD_WIN32` CMake option for enabling Win32 support (#1958)
  - Added `GLFW_BUILD_COCOA` CMake option for enabling Cocoa support (#1958)
  - Added `GLFW_BUILD_X11` CMake option for enabling X11 support (#1958)

include/GLFW/glfw3native.h

@@ -74,6 +74,16 @@ extern "C" {
  *  and which platform-specific headers to include.  It is then up your (by
  *  definition platform-specific) code to handle which of these should be
  *  defined.
+ *
+ *  If you do not want the platform-specific headers to be included, define
+ *  `GLFW_NATIVE_INCLUDE_NONE` before including the @ref glfw3native.h header.
+ *
+ *  @code
+ *  #define GLFW_EXPOSE_NATIVE_WIN32
+ *  #define GLFW_EXPOSE_NATIVE_WGL
+ *  #define GLFW_NATIVE_INCLUDE_NONE
+ *  #include <GLFW/glfw3native.h>
+ *  @endcode
  */
 
 
@@ -81,6 +91,8 @@ extern "C" {
  * System headers and types
  *************************************************************************/
 
+#if !defined(GLFW_NATIVE_INCLUDE_NONE)
+
  #if defined(GLFW_EXPOSE_NATIVE_WIN32) || defined(GLFW_EXPOSE_NATIVE_WGL)
   /* This is a workaround for the fact that glfw3.h needs to export APIENTRY (for
    * example to allow applications to correctly declare a GL_KHR_debug callback)
@@ -137,6 +149,8 @@ extern "C" {
   #include <GL/osmesa.h>
  #endif
 
+#endif /*GLFW_NATIVE_INCLUDE_NONE*/
+
 
 /*************************************************************************
  * Functions