swift234

[driver] Added a separate Parseable OutputLevel.

This level is selected by -parseable-output. This flag is only accepted by
swiftc, since it does not make sense for any of the interactive modes.
(Currently, this level prints out the same information as Verbose, with a
"Command: " string prepended.)

Additionally, in Compilation::performJobs, set RequiresBufferedOutput to true if
parseable output was requested, since parseable output will require buffered
output.

Part of <rdar://problem/15958329>.

Swift SVN r20872