Xz.git: Fix Linux Landlock Feature Test in Autotools

[michelangelo]

This is just spectacular. Evil, of course, but spectacular nevertheless.

  +        #include <sys/prctl.h>
  +. <<<<<<<<<<<<<<<<<<<<<<<< THIS IS IT
  +        void my_sandbox(void)
  +        {
  +

[fargle]

why bother with a . instead of a &nbsp or some other unicode hackdodgery?

[atombender]

Thread from yesterday (221 comments): https://news.ycombinator.com/item?id=39874404

[jamespwilliams]

Can you spot the intentional bug in this commit?

[JSDevOps]

It was checking if the C compiled to detect the landlock feature, and there was a single character in the middle of the code that made it always fail to compile and therefore silently leave the feature disabled.