Rustc did recently get a "x86-interrupt" calling convention, but that's unrelated to #[no_std], and only works on x86. Either way, "#pragma interrupt" should work just as well in C++ as in C, since C++ doesn't really change any aspect of the language that matters there.

Further, even in C I rarely see use of "#pragma interrupt"-like tools- rather, everyone still seems just to use per-platform assembly glue code. (To be fair, my experience is mostly in kernel code for things like Linux, rather than standalone embedded applications where "#pragma interrupt" would be more valuable.)