swift234

[driver] Added support for the '--driver-mode=' flag.

There are two valid values for this: 'swift' and 'swiftc'. This flag must be
specified as the first option; otherwise, it will be ignored. This flag allows
the caller of the driver to force 'swift' to behave as 'swiftc', or vice versa,
and is useful in situations where the name of the executable cannot be changed.

Swift SVN r20656