swift234

Parse: Update parsing of #available(...) to no longer user >= version comparison

Change the syntax of availability queries from #available(iOS >= 8.0, OSX >= 10.10, *) to

This change reflects the fact that now that we spell the query '#available()' rather than
'#os()', the specification is about availability of the APIs introduced in a particular OS
release rather than an explicit range of OS versions on which the developer expects the
code to run.

There is a Fix-It to remove '>=' to ease adopting the new syntax.

Swift SVN r28025