swift234

Runtime: Allow protocol extensions for weakly-linked Objective-C classes

Change ProtocolConformanceRecord::getCanonicalTypeMetadata() to return null if
the class metadata in the protocol conformance record is null. This fixes a
runtime crash in swift_conformsToProtocol when there is a protocol extension of
a missing weakly-linked class.

rdar://problem/21541766

Swift SVN r30012