This is how they behave in LDC at the moment. If you can come up with a more consistent/intuitive setup, please make a ticket.

• ldc somefile.d
  • output somefile.o
  • link somefile unless -c

• ldc somefile.d <ouput switches>
  • output somefile.*
  • link somefile if .o is output and not -c

• ldc somefile.d -of<name>
  • output name.o
  • link name

• ldc -c somefile.d -of<name>.<ext>
  • if ext is known, output name.ext of correct type
  • if ext is unknown, output name.ext.o object file

• ldc somefile.d -of<name> <output switches>
  • output name.*
  • link name if .o is output

• ldc -c somefile.d -of<name>.<ext> <output switches>
  • if ext is known, output name.ext of correct type and name.*
  • if ext is unknown, output name.ext.*

TODO: Add cases for multiple source files.