Update array type regex to account for missing whitespace

[pema99]

On my machine, using Futhark 0.19.7, the compiler does not emit a space after the declaration of an array type.
This in turn causes the array_types Vec in the code I changed to become empty, and crucial machinery for array types is never generated.

This happens even when using the simple example in examples/. I've attached the full output of that example using sequential_c, see line 49 for an example.

This change just makes that whitespace optional in the regex.

[Erk-]

Thanks!

[Erk-]

I have published a new version with this fix