swift234

[ClangImporter] Ignore deprecated enum constants when computing prefixes.

This fixes the import of enums like NSCalendarUnit, which changed from
NSXXXCalendarUnit to NSCalendarUnitXXX, as has been the guideline in
recent years. Now even when the old names are present, we can still
prefix-strip based on the new names. If /all/ options are deprecated,
though, we'll prefix-strip as we did before.

Note that we /don't/ check the current deployment target for this,
because we want to use the "nice" names as soon as we have an SDK where
they're available, not when the deployment target matches such an SDK.

rdar://problem/17686122

Swift SVN r26184