The fast kernel headers tree

That's going to put a substantial drop in performance in my post-retirement plan to modify gcc to use openat for -I directives instead of concatenating each of the -I paths and trying to open the files from root, which cuts out a number of inode lookups and the string concatenation. I doubt it would have improved performance more than a few percent, and now there will be a lot fewer files to open. At least for the kernel, anyway, it could still help other compilations. But, someone may beat me to the change, or perhaps someone has already done it.