[common-dylan] Fix x86_64-darwin cli arguments.

The 'mib' that we pass to sysctl is an array of ints, not longs,
so make sure that we're using 4 bytes per entry rather than word
size.
[common-dylan] Fix isize type in sysctl calls.

The isize parameter is a <raw-c-unsigned-int>, not a <raw-byte-string>,
so use the right type. This was wrong before, but harmless, but the
LLVM backend is thankfully stricter about this.

Thanks to @housel for pointing this out.
Merge pull request #585 from waywardmonkeys/fix-x86-64-darwin-command-line-arguments

[common-dylan] Fix x86_64-darwin cli arguments.