I've seen style guides recommend that to avoid typos on == that accidentally result in assignment: write "123 == foo" instead of "foo == 123" so that you can't accidentally write "foo = 123".
It's not only about not accidentally writing `if (x=0)`.
The `if (0==x)` style also makes it obvious that the check is correct when reviewing/reading code. Sure, a linter might catch this. But this way the reader doesn't need to rely on that. Besides many codebases allow variable assignment as part of conditional/loop expressions, and sometimes sadly it's easier to write code this way than to get a team to use a linter.
Regarding it being unnatural... you get used to it, and especially in C one needs to take care to check the return code the right way (0!=, 0==, -1!=, 0<, !, etc.), whereas the other side of the check is often more straightforward (a function call, a variable etc.), so it's nice to have the constant up front. It takes very little extra space at the front. As a bonus all the constants will visually line up nicely that way.
> Surely such code would be caught by some other tool
This technique was invented back in the 1980s, back then compilers have no static analysis capabilities that we take for granted today. I think the reason of keep using it in 2020 is a matter of habit.
