Don't suspend warnings without position
Don't suspend warnings without position

In `@nowarn` support, don't suspend warnings without positions.

Typer inspects all `@nowarn` annotations in a file ("suppressions").
Warnings reported before typer are suspended (buffered) so they
can later be filtered.

Warnings without a position are never filtered, so they should be
reported directly. Currently, they are reported thanks to
`reportSuspendedMessages` which is invoked at the very end of
a compilation run.

scala/scala,lrytz/scala,scala/scala,scala/scala,scala/scala,lrytz/scala,lrytz/scala,scala/scala,lrytz/scala,lrytz/scala,lrytz/scala,scala/scala