compat/macos: fix methods from 'development_tools'

The previous fixes in c6dc50fc and
ed9f7308 were incomplete as they
referenced `DeveloperTools`, but the actual name is `DevelopmentTools`.

Also fixes indentation and a broken `MacOS.clang_version` (it was
falsely redirecting to `DeveloperTools.llvm_build_version` ).

References #219.
References #220.