Filter fdump-passes output from stderr before displaying (#3115)
Filter fdump-passes output from stderr before displaying (#3115)

The refactor from #3024 left all the output from -fdump-passes in
stderr. Filter it out before displaying it in the output pane.

Signed-off-by: Marc Poulhiès <3159a46716b78b3b6c7634a90e9d5898d5f4255e@kataplop.net>
mattgodbolt/compiler-explorer,mattgodbolt/compiler-explorer,mattgodbolt/compiler-explorer,mattgodbolt/compiler-explorer,mattgodbolt/compiler-explorer,mattgodbolt/compiler-explorer,mattgodbolt/compiler-explorer,mattgodbolt/compiler-explorer