Nuri Amari 86c5698780 Implement importing of forward declared objc protocols and interfaces ...

This modifies the ClangImporter to introduce an opaque placeholder
representation for forward declared Objective-C interfaces and
protocols when imported into Swift.

In the compiler, the new functionality is hidden behind a frontend
flag -enable-import-objc-forward-declarations, and is on by default
for language mode >6.

The feature is disabled entirely in LLDB expression evaluation / Swift
REPL, regardless of language version.

2023-03-07 16:00:16 -08:00

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ForwardDeclarations

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