[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/pixel.h

@@ -0,0 +1,83 @@
+/* $Id: pixel.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: pixel.h,v $
+ * Revision 1.1  1996/09/13 01:38:16  brianp
+ * Initial revision
+ *
+ */
+
+
+#ifndef PIXEL_H
+#define PIXEL_H
+
+
+#include "types.h"
+
+
+extern void gl_GetPixelMapfv( GLcontext *ctx, GLenum map, GLfloat *values );
+
+extern void gl_GetPixelMapuiv( GLcontext *ctx, GLenum map, GLuint *values );
+
+extern void gl_GetPixelMapusv( GLcontext *ctx, GLenum map, GLushort *values );
+
+
+extern void gl_PixelMapfv( GLcontext *ctx,
+                           GLenum map, GLint mapsize, const GLfloat *values );
+
+extern void gl_PixelStorei( GLcontext *ctx, GLenum pname, GLint param );
+
+extern void gl_PixelTransferf( GLcontext *ctx, GLenum pname, GLfloat param );
+
+extern void gl_PixelZoom( GLcontext *ctx, GLfloat xfactor, GLfloat yfactor );
+
+
+extern GLvoid *gl_unpack_pixels( GLcontext *ctx,
+                                 GLsizei width, GLsizei height,
+                                 GLenum format, GLenum type,
+                                 const GLvoid *pixels );
+
+
+extern void
+gl_write_zoomed_color_span( GLcontext *ctx,
+                            GLuint n, GLint x, GLint y, const GLdepth z[],
+                            const GLubyte red[], const GLubyte green[],
+                            const GLubyte blue[], const GLubyte alpha[],
+                            GLint y0 );
+
+
+extern void
+gl_write_zoomed_index_span( GLcontext *ctx,
+                            GLuint n, GLint x, GLint y, const GLdepth z[],
+                            const GLuint indexes[], GLint y0 );
+
+
+extern void
+gl_write_zoomed_stencil_span( GLcontext *ctx,
+                              GLuint n, GLint x, GLint y,
+                              const GLubyte stencil[], GLint y0 );
+
+
+#endif
+