swift

3ce7a746 - Ask SILFunction link entities' clang nodes for weakness when applicable (#2822)

Ask SILFunction link entities' clang nodes for weakness when applicable (#2822) * Provide ways to get back to the original Clang declaration from a SILFunction or SILGLobalVariable. This will be used as one step towards moving IRGen off of the global external-definitions list. * Ask SILFunction link entities' clang nodes for weakness when applicable When importing C functions with availability attributes, we don't properly use that information to decide whether a symbol should be weak_extern, causing load failures in dylibs that reference these symbols when deployed to an older OS. This is a very targeted fix and we need a better architecture for deciding this. rdar://problem/26359452