Use Xcode. The kext you posted as a zip-file has an Xcode project, so I don't know why this wouldn't be obvious.
Sign up at the free (non-paying) level as an Apple Developer. Then sign in using that account and download the version of Xcode appropriate for your OS version.
Older versions of Xcode, i.e. the 3.* and earlier version numbers, are freely available as downloads from the Apple Developer Center. To find them:
1. Login at:
https://developer.apple.com/devcenter/mac/index.action
2. Click the "View all downloads" link.
3. Type
xcode or
xcode 3 in the search box.
Each individual version of Xcode download should list what the minimum OS version is. You can also read Xcode release notes to find which Xcode version was the last one to have PPC-targeted compilers.