I lost 30 minutes of my life today to:

```yaml
env:
  RUSTFLAGS: "-Dwarnings" 
```

in github CI, causing cargo to **completely ignore** this in my `.cargo/config.toml`:

```toml
[target.thumbv7em-none-eabihf]
rustflags = [
    "-Clink-arg=-Tlink.x",
    "-Clink-arg=-Tdefmt.x",
]
```

Those `rustflags` are **load bearing** and a lot of weird stuff will happen if you don't have them.

I wish cargo was better at *merging* rustflags rather than entirely replacing them.