swift234

[driver] Added initial support for loading an OutputFileMap.

Added an -output-file-map option which will specify the path to an
OutputFileMap.

Added Driver::buildOutputFileMap(), which constructs an OutputFileMap
from the arguments.

Added OutputFileMap* parameters to Driver::buildJobs() and
Driver::buildJobsForAction(). (These parameters are not yet honored, except to
pass to calls of these functions.)

Swift SVN r12772