`bsr` has changed since the last update

[ISSOtm]

If the content source operand is 0, the content of the destination operand is undefined.

(https://www.felixcloutier.com/x86/bsr)

But as of today, upstream reads:

If the content source operand is zero, the destination operand is unmodified.

I stumbled upon this while trying to make sense of this Godbolt.

Thank you very much for your work, btw!