Completely ignore the commented lines while inserting pragmas

The idea is that you probably want to be able to comment
the choice of pragmas some time without disrupting the workflow of
enabling and disabling them.

Nobody uses multiline comments though, so they aren't ignored
but instead still break everything
CPP pragma should always be at the top

The reason for that is inability to use the pre-processor
to conditionally enable extensions unless -XCPP itself is enabled.