Unable to build electrs on Odroid HC2

This issue is a problem I encountered with [your electrs fork](https://github.com/Blockstream/electrs/pulls) -- but that repo doesn't accept issues so I'm posting here.

I get an error when I run the build command described in the directions:

```
$ cargo run --release --bin electrs -- -vvvv --daemon-dir ~/.bitcoin
Downloaded cc v1.0.25
...
Compiling crossbeam-utils v0.6.1
Compiling rayon-core v1.4.1
error: failed to run custom build command for `rayon-core v1.4.1`
could not execute process `/mnt/hdd2/electrs/target/release/build/rayon-core-ce94679caf3f5155/build-script-build` (never executed)
warning: build failed, waiting for other jobs to finish...
error: build failed
```

I can run the same command from the [base romanz/electrs project](https://github.com/romanz/electrs) and it builds successfully.

So I don't believe it's an upstream problem. But I lack the rust chops to debug exactly what is failing ...