swift234

[Driver] Reject SDKs older than OS X 10.10 or iOS 8.

Actually, reject SDK directories whose names match
  "*OSX<version>(.Internal)?.sdk" on OS X with a version older than 10.10
  "*OS7*" on iOS
  "*Simulator7*" on iOS

We only really care about 10.9 anyway, but just in case people install the
one-previous version of iOS...

<rdar://problem/17951615>

Swift SVN r21100