swift234

[ClangImporter] Restore typealiases for NSInteger, size_t, etc.

We will still import these as just 'Int', 'UInt', etc., but we still want to
allow users to write some of these types themselves. We now have an enum field
in MappedTypes.def to control this.

Fix-up for r14069 and <rdar://problem/16067854>

Swift SVN r14105