[OPENGL32][MESA] Downgrade Mesa library to version 2.6

With this commit, we now use a forked version of MESA which only supports OpenGL 1.1, like the windows implementation does.
It exposes :
  - The same pixel formats
  - The same set of extensions
  - Nothing more
All of this without taking 10% of your build time.
If you need a more modern option, look at the MESA package from Rapps, which is (and must be) maintained outside of this code tree.
CORE-7499

dll/opengl/mesa/bitmap.h

@@ -0,0 +1,59 @@
+/* $Id: bitmap.h,v 1.1 1996/09/13 01:38:16 brianp Exp $ */
+
+/*
+ * Mesa 3-D graphics library
+ * Version:  2.0
+ * Copyright (C) 1995-1996  Brian Paul
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with this library; if not, write to the Free
+ * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+
+/*
+ * $Log: bitmap.h,v $
+ * Revision 1.1  1996/09/13 01:38:16  brianp
+ * Initial revision
+ *
+ */
+
+
+#ifndef BITMAP_H
+#define BITMAP_H
+
+
+#include "types.h"
+
+
+extern struct gl_image *gl_unpack_bitmap( GLcontext* ctx,
+                                          GLsizei width, GLsizei height,
+                                          const GLubyte *bitmap );
+
+
+
+extern void gl_render_bitmap( GLcontext* ctx,
+                              GLsizei width, GLsizei height,
+                              GLfloat xorig, GLfloat yorig,
+                              GLfloat xmove, GLfloat ymove,
+                              const struct gl_image *bitmap );
+
+
+extern void gl_Bitmap( GLcontext* ctx,
+                       GLsizei width, GLsizei height,
+                       GLfloat xorig, GLfloat yorig,
+                       GLfloat xmove, GLfloat ymove,
+                       const struct gl_image *bitmap );
+
+
+#endif