Don't hardcode compiler and arch.

For compiler use `"COMP=#{ENV.cc"`

For arch, you'll want to use something like this:

```ruby
arch = if Hardware::CPU.type == :intel
  Hardware::CPU.bits == 32 ? 'i386' : 'x86_64'
else
  Hardware::CPU.bits == 32 ? 'ppc' : 'ppc64'
```

(Or whatever arch formats it supports)