win32: Minor build fixes for building for win32

This fixes some minor errors and warnings that were preventing Cogl
building with mingw32:

• cogl-framebuffer-gl.c was not including cogl-texture-private.h.
  Presumably something else ends up including that when building for
  GLX.

• The WGL winsys was not including cogl-error-private.h

• A call to strsplit in the WGL winsys was wrong.

• For some reason the test-wrap-rectangle-textures test was trying to
  include the GDKPixbuf header.

Reviewed-by: Robert Bragg <robert@linux.intel.com>

(cherry picked from commit 5380343399f834d9f96ca3b137d49c9c2193900a)

cogl/driver/gl/cogl-framebuffer-gl.c

@@ -33,6 +33,7 @@
 #include "cogl-buffer-gl-private.h"
 #include "cogl-error-private.h"
 #include "cogl-texture-gl-private.h"
+#include "cogl-texture-private.h"
 
 #include <glib.h>
 #include <string.h>

cogl/winsys/cogl-winsys-wgl.c

@@ -45,6 +45,7 @@
 #include "cogl-feature-private.h"
 #include "cogl-win32-renderer.h"
 #include "cogl-winsys-wgl-private.h"
+#include "cogl-error-private.h"
 
 typedef struct _CoglRendererWgl
 {
@@ -617,7 +618,8 @@ update_winsys_features (CoglContext *context, CoglError **error)
 
   if (wgl_extensions)
     {
-      char **split_extensions = g_strsplit (wgl_extensions);
+      char **split_extensions =
+        g_strsplit (wgl_extensions, " ", 0 /* max_tokens */);
 
       COGL_NOTE (WINSYS, "  WGL Extensions: %s", wgl_extensions);
 
@@ -644,9 +646,7 @@ update_winsys_features (CoglContext *context, CoglError **error)
 static CoglBool
 _cogl_winsys_context_init (CoglContext *context, CoglError **error)
 {
-  CoglContextWgl *wgl_context;
-
-  wgl_context = context->winsys = g_new0 (CoglContextWgl, 1);
+  context->winsys = g_new0 (CoglContextWgl, 1);
 
   cogl_win32_renderer_add_filter (context->display->renderer,
                                   win32_event_filter_cb,

tests/conform/test-wrap-rectangle-textures.c

@@ -1,5 +1,4 @@
 #include <cogl/cogl.h>
-#include <gdk-pixbuf/gdk-pixbuf.h>
 
 #include <string.h>