(this probably affects other systems, not just W32, but i only have W32, so here you go...)

In file included from ../../../../gst-libs/gst/gl/gstgl_fwd.h:26:0,
                 from ../../../../gst-libs/gst/gl/gl.h:24,
                 from gstglwindow_win32.h:24,
                 from gstglwindow_win32.c:26:
../../../../gst-libs/gst/gl/glprototypes/gles1gles2.h:59:23: error: unknown type name 'GLeglImageOES'
                       GLeglImageOES    image))
                       ^
../../../../gst-libs/gst/gl/gstglapi.h:84:24: note: in definition of macro 'GST_GL_EXT_FUNCTION'
   ret GSTGLAPI (*name) args;
                        ^
../../../../gst-libs/gst/gl/glprototypes/gles1gles2.h:62:23: error: unknown type name 'GLeglImageOES'
                       GLeglImageOES    image))
                       ^
../../../../gst-libs/gst/gl/gstglapi.h:84:24: note: in definition of macro 'GST_GL_EXT_FUNCTION'
   ret GSTGLAPI (*name) args;
                        ^
make[5]: *** [libgstgl_win32_la-gstglwindow_win32.lo] Error 1

The type GLeglImageOES is from GLES/glext.h and is not present in any of the GL/*.h headers. In GLES/glext.h it is defined like this:

/* GL_OES_EGL_image */
#ifndef GL_OES_EGL_image
typedef void* GLeglImageOES;
#endif
...
/* GL_OES_EGL_image */
#ifndef GL_OES_EGL_image
#define GL_OES_EGL_image 1
...


A quick-and-dirty way to fix this is to add

#ifndef GL_OES_EGL_image
typedef void* GLeglImageOES;
#endif
to gstglapi.h (after all GL and/or GLES headers are included)

The type is used in the prototypes of EGLImageTargetTexture2D and EGLImageTargetRenderbufferStorage.

Considering the fact that they come from gles1gles2.h (that is, functions that are only available in GLES, not in GL), it's clearly wrong to even consider them when GLES is not available. Why the contents of gles1.h, gles1gles2.h and gles2.h aren't under appropriate #ifdef?