We already have an option to skip /all/ unavailable decls. Singling
out the ones that are specifically unavailable-in-Swift just makes
testing harder.
This will not affect interface generation in Xcode, which sets that
option to skip all unavailable decls.
This applies the same fix as cfdb8ac2e61, but this time to libIDE so
that SourceKit and swift-ide-test will also pass in an appropriate
argv[0]. Re-enable the tests that broke.
rdar://problem/24431137
Enum constants are naturally going to be named after their ObjC name,
not their Swift name. As such, ignore the swift_name attr on the enum
decl when calculating the common prefix. It turns out this is actually
simpler anyway as it also bypasses the swift_private handling that the
code was already trying to work around.
