and how, pray tell, are intrinsics implemented?

The JIT compiler reckognizes them and give special meaning, see linked article.

i was being rhetorical, the intrinsics are implemented in native code

From Java code AOT compiled into native code, better learn about compilers instead of being rhetorical.

We're literally saying the same thing. Java compiled into a native code library for each target with intrinsics that give access to things like CPU registers is just another way of implementing intrinsics in native code

And native code is not C or C++? How do you think the very first C compiler were written? Spoiler, it was bootstrapped with assembly which was bootstrapped with machine code.