With bitcode enabled, the XCTest overlay fails to link because
XCTest.framework itself was not built with bitcode. For now, we should
not build this overlay with bitcode. It isn't embedded in apps.
rdar://problem/20884313
Swift SVN r28355
The standard library has grown significantly, and we need a new
directory structure that clearly reflects the role of the APIs, and
allows future growth.
See stdlib/{public,internal,private}/README.txt for more information.
Swift SVN r25876