D42892 changed a lot of code to use superclass DWARFUnit instead of its subclass DWARFCompileUnit.
Finish this change more thoroughly for any *CompileUnit*->*Unit* names. Later patch will introduce DWARFTypeUnit which needs to be sometimes different from DWARFCompileUnit and it would be confusing without this renaming.
The whole patchset available for testing as: git clone -b debugtypes git://git.jankratochvil.net/lldb