[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/context.h

@@ -0,0 +1,179 @@
+/* $Id: context.h,v 1.9 1997/09/29 22:25:28 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: context.h,v $
+ * Revision 1.9  1997/09/29 22:25:28  brianp
+ * added const to a few function parameters
+ *
+ * Revision 1.8  1997/05/26 21:14:13  brianp
+ * gl_create_visual() now takes red/green/blue/alpha_bits arguments
+ *
+ * Revision 1.7  1997/04/16 23:55:06  brianp
+ * added gl_set_api_table()
+ *
+ * Revision 1.6  1997/04/12 17:12:43  brianp
+ * added gl_get_current_context()
+ *
+ * Revision 1.5  1997/02/27 19:57:38  brianp
+ * added gl_problem() function
+ *
+ * Revision 1.4  1997/02/10 19:49:50  brianp
+ * added gl_ResizeBuffersMESA()
+ *
+ * Revision 1.3  1996/09/19 03:14:49  brianp
+ * now just one parameter for gl_create_framebuffer()
+ *
+ * Revision 1.2  1996/09/15 14:20:22  brianp
+ * added new functions for GLframebuffer and GLvisual support
+ *
+ * Revision 1.1  1996/09/13 01:38:16  brianp
+ * Initial revision
+ *
+ */
+
+
+#ifndef CONTEXT_H
+#define CONTEXT_H
+
+
+#include "types.h"
+
+
+
+#ifdef THREADS
+   /*
+    * A seperate GLcontext for each thread
+    */
+   extern GLcontext *gl_get_thread_context( void );
+#else
+   /*
+    * All threads use same pointer to current context.
+    */
+   extern GLcontext *CC;
+#endif
+
+
+
+/*
+ * There are three Mesa datatypes which are meant to be used by device
+ * drivers:
+ *   GLcontext:  this contains the Mesa rendering state
+ *   GLvisual:  this describes the color buffer (rgb vs. ci), whether
+ *              or not there's a depth buffer, stencil buffer, etc.
+ *   GLframebuffer:  contains pointers to the depth buffer, stencil
+ *                   buffer, accum buffer and alpha buffers.
+ *
+ * These types should be encapsulated by corresponding device driver
+ * datatypes.  See xmesa.h and xmesaP.h for an example.
+ *
+ * The following functions create and destroy these datatypes.
+ */
+
+
+/*
+ * Create/destroy a GLvisual.  A GLvisual is like a GLX visual.  It describes
+ * the colorbuffer, depth buffer, stencil buffer and accum buffer which will
+ * be used by the GL context and framebuffer.
+ */
+extern GLvisual *gl_create_visual( GLboolean rgb_flag,
+                                   GLboolean alpha_flag,
+                                   GLboolean db_flag,
+                                   GLint depth_bits,
+                                   GLint stencil_bits,
+                                   GLint accum_bits,
+                                   GLint index_bits,
+                                   GLfloat red_scale,
+                                   GLfloat green_scale,
+                                   GLfloat blue_scale,
+                                   GLfloat alpha_scale,
+                                   GLint red_bits,
+                                   GLint green_bits,
+                                   GLint blue_bits,
+                                   GLint alpha_bits );
+
+extern void gl_destroy_visual( GLvisual *vis );
+
+
+/*
+ * Create/destroy a GLcontext.  A GLcontext is like a GLX context.  It
+ * contains the rendering state.
+ */
+extern GLcontext *gl_create_context( GLvisual *visual,
+                                     GLcontext *share_list,
+                                     void *driver_ctx );
+
+extern void gl_destroy_context( GLcontext *ctx );
+
+
+/*
+ * Create/destroy a GLframebuffer.  A GLframebuffer is like a GLX drawable.
+ * It bundles up the depth buffer, stencil buffer and accum buffers into a
+ * single entity.
+ */
+extern GLframebuffer *gl_create_framebuffer( GLvisual *visual );
+
+extern void gl_destroy_framebuffer( GLframebuffer *buffer );
+
+
+
+extern void gl_make_current( GLcontext *ctx, GLframebuffer *buffer );
+
+extern GLcontext *gl_get_current_context(void);
+
+extern void gl_copy_context(const GLcontext *src, GLcontext *dst, GLuint mask);
+
+extern void gl_set_api_table( GLcontext *ctx, const struct gl_api_table *api );
+
+
+
+/*
+ * GL_MESA_resize_buffers extension
+ */
+extern void gl_ResizeBuffersMESA( GLcontext *ctx );
+
+
+
+/*
+ * Miscellaneous
+ */
+
+extern void gl_problem( const GLcontext *ctx, const char *s );
+
+extern void gl_warning( const GLcontext *ctx, const char *s );
+
+extern void gl_error( GLcontext *ctx, GLenum error, const char *s );
+
+extern GLenum gl_GetError( GLcontext *ctx );
+
+
+extern void gl_update_state( GLcontext *ctx );
+
+
+
+#ifdef PROFILE
+extern GLdouble gl_time( void );
+#endif
+
+
+#endif