mesa: add PrimitiveRestartInSoftware to gl_context.Const

If set, then the VBO module will handle all primitive
restart scenarios before calling the driver draw_prims.

Software primitive restart support is disabled by default.

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/mesa/main/context.c

@@ -662,6 +662,9 @@ _mesa_init_constants(struct gl_context *ctx)
 
    /* GL_ARB_robustness */
    ctx->Const.ResetStrategy = GL_NO_RESET_NOTIFICATION_ARB;
+
+   /* PrimitiveRestart */
+   ctx->Const.PrimitiveRestartInSoftware = GL_FALSE;
 }