This allows us to mark this flag as DoesNotAffectIncrementalBuild, so
that switching between a tty and non-tty doesn't cause full rebuilds
with swiftpm.
https://bugs.swift.org/browse/SR-7982
Most tests were using %swift or similar substitutions, which did not
include the target triple and SDK. The driver was defaulting to the
host OS. Thus, we could not run the tests when the standard library was
not built for OS X.
Swift SVN r24504
Most of the tests just got moved to swiftc, but some of them were
duplicated to apply to both swiftc and swift. A handful still use the
existing 'swift' because they are for the existing '-i' syntax.
Note: this means config.swift_driver now uses the staging symlink
'swifti'. The only thing preventing us from dropping the 'i' and getting
rid of the old interface is that Xcode hasn't moved to swiftc yet
<rdar://problem/17769327>.
Swift SVN r20467
Previously, the frontend detected that its output was being piped into the
driver and buffered, and decided that that wasn't a color-friendly output
stream. Now, the driver passes -color-diagnostics to the frontend to force
color output if the driver itself is in a color-output context.
<rdar://problem/16697713>
Swift SVN r18506
