bug#69106: SBCL enomem on 686

[Christopher Howard]

Hi, the problem is with these lines:

```
                     ,@(if (target-ppc32?)
                         ;; 3072 is too much for this architecture.
                         `("--dynamic-space-size=2048")
                         `("--dynamic-space-size=3072"))
```

Package definition simply assumes that all non-ppc32 architectures can handle 
the larger dynamic space, but apparently not x86. Through experiment, I see the 
largest dynamic space that works on my old laptop is 2810, but 2048 seems like 
a more sensible number.

-- 
Christopher Howard