Fix "compilation" warnings

[raphaelmeyer]

There are a few compilation warnings that should be fixed.

warning: [options] source value 7 is obsolete and will be removed in a future release
warning: [options] target value 7 is obsolete and will be removed in a future release
warning: [options] To suppress warnings about obsolete options, use -Xlint:-options.
Note: Some input files use or override a deprecated API.
Note: Recompile with -Xlint:deprecation for details.

[imavroukakis]

👋 may I have a go at cleaning this up?