I'm not sure what's causing this problem with jemalloc but I can reproduce it.
In the meantime, you can cross compile your binaries against the system allocator. Or at least, that's working for me.
// hello.rs
#![feature(alloc_system)]
extern crate alloc_system;
fn main() {
println!("Hello, world!");
}
$ rustc --target=mips-unknown-linux-gnu -C linker=mips-openwrt-linux-gcc hello.rs && echo OK
'generic' is not a recognized processor for this target (ignoring processor)
...
OK