Issues with floating-point atomics

I run my code under oneAPI on dawn (Cambridge, UK) and 

for a kernel with

```
@atomic :monotonic M[Iz,ind,1] += JJ[ID,1,Iz,IF]
```

we get the error 

```
ERROR: LoadError: Failed to translate LLVM code to SPIR-V.
RequiresExtension: Feature requires the following SPIR-V extension:
 SPV_EXT_shader_atomic_float_add
```