swift234

Revert several commits working around the autolinking breakage.

Swift was failing to autolink frameworks in the new text-based SDKs.
Clang r253060 fixes the underlying issue, so we can go back to relying
on autolinking for these.

This reverts the following commits (newest to oldest):
f658841
59092a3
7ea9d54
e52ef22

rdar://problem/23511008