[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/config.h

@@ -0,0 +1,167 @@
+/* $Id: config.h,v 1.8 1997/09/27 00:13:44 brianp Exp $ */
+
+/*
+ * Mesa 3-D graphics library
+ * Version:  2.5
+ * Copyright (C) 1995-1997  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: config.h,v $
+ * Revision 1.8  1997/09/27 00:13:44  brianp
+ * added GL_EXT_paletted_texture extension
+ *
+ * Revision 1.7  1997/09/23 00:57:21  brianp
+ * removed MAX_DISPLAYLISTS
+ *
+ * Revision 1.6  1997/06/17 02:20:25  brianp
+ * changed MAX_WIDTH to 1600 and MAX_HEIGHT to 1200
+ *
+ * Revision 1.5  1997/05/28 03:27:19  brianp
+ * set MAX_TEXTURE_LEVELS to 9 if compiling for 3Dfx driver (FX)
+ *
+ * Revision 1.4  1997/01/08 20:54:02  brianp
+ * added DITHER666 option from Michael Pichler
+ *
+ * Revision 1.3  1996/10/01 03:30:18  brianp
+ * changed MAX_DEPTH to 0x00ffffff for 32-bit depth buffer
+ *
+ * Revision 1.2  1996/09/15 01:49:26  brianp
+ * removed some junk
+ *
+ * Revision 1.1  1996/09/13 01:38:16  brianp
+ * Initial revision
+ *
+ */
+
+
+
+/*
+ * Tunable configuration parameters.
+ */
+
+
+
+#ifndef CONFIG_H
+#define CONFIG_H
+
+
+
+/* Maximum modelview matrix stack depth: */
+#define MAX_MODELVIEW_STACK_DEPTH 32
+
+/* Maximum projection matrix stack depth: */
+#define MAX_PROJECTION_STACK_DEPTH 32
+
+/* Maximum texture matrix stack depth: */
+#define MAX_TEXTURE_STACK_DEPTH 10
+
+/* Maximum attribute stack depth: */
+#define MAX_ATTRIB_STACK_DEPTH 16
+
+/* Maximum client attribute stack depth: */
+#define MAX_CLIENT_ATTRIB_STACK_DEPTH 16
+
+/* Maximum recursion depth of display list calls: */
+#define MAX_LIST_NESTING 64
+
+/* Maximum number of lights: */
+#define MAX_LIGHTS 8
+
+/* Maximum user-defined clipping planes: */
+#define MAX_CLIP_PLANES 6
+
+/* Number of texture levels */
+#define MAX_TEXTURE_LEVELS 11
+
+/* Max texture size */
+#define MAX_TEXTURE_SIZE   (1 << (MAX_TEXTURE_LEVELS-1))
+
+/* Maximum pixel map lookup table size: */
+#define MAX_PIXEL_MAP_TABLE 256
+
+/* Number of auxillary color buffers: */
+#define NUM_AUX_BUFFERS 0
+
+/* Maximum order (degree) of curves: */
+#ifdef AMIGA
+#   define MAX_EVAL_ORDER 12
+#else
+#   define MAX_EVAL_ORDER 30
+#endif
+
+/* Maximum Name stack depth */
+#define MAX_NAME_STACK_DEPTH 64
+
+/* Min and Max point sizes and granularity */
+#define MIN_POINT_SIZE 1.0
+#define MAX_POINT_SIZE 10.0
+#define POINT_SIZE_GRANULARITY 0.1
+
+/* Min and Max line widths and granularity */
+#define MIN_LINE_WIDTH 1.0
+#define MAX_LINE_WIDTH 10.0
+#define LINE_WIDTH_GRANULARITY 1.0
+
+/* Max texture palette size */
+#define MAX_TEXTURE_PALETTE_SIZE 256
+
+
+/* Maximum viewport size: */
+#ifdef AMIGA
+#  define MAX_WIDTH 640
+#  define MAX_HEIGHT 400
+#else
+#  define MAX_WIDTH 1600
+#  define MAX_HEIGHT 1200
+#endif
+
+
+
+/*
+ * Bits per accumulation buffer color component:  8 or 16
+ */
+#define ACCUM_BITS 16
+
+
+/*
+ * Bits per depth buffer value:  16 or 32
+ */
+#define MAX_DEPTH 0x00ffffff
+#define DEPTH_SCALE ((GLfloat) 0x00ffffff)
+
+
+/*
+ * Bits per stencil value:  8
+ */
+#define STENCIL_BITS 8
+
+
+
+/***
+ *** For X11 driver only:
+ ***/
+
+/*
+ * When defined, use 6x6x6 dithering instead of 5x9x5.
+ * 5x9x5 better for general colors, 6x6x6 better for grayscale.
+ */
+/*#define DITHER666*/
+
+
+#endif