[cxx-interop] Break when we find a linkage specification when traversing all decls in IRGen.

[zoecarver]

Without this, we will find the linkage specification decl rather than a function decl (for example). The problem here is that we will check if we've already traversed this decl and bail out. If we do that we will not codegen the function decl (for example) and get linker errors.

I have a test case that I'm trying to reduce and I will add that as a test. rdar://110439422

[zoecarver]

extern "C" {

inline void inlineFn();

void cacheMis();
void incorrectCacheHit() {
  inlineFn();
}

static void caller() {  
  cacheMis();
  incorrectCacheHit();
}

inline void inlineFn() {
}

}

// Swift

public func test() {
  caller()
}

[plotfi]

@zoecarver Ah so this is to keep the ClangDeclFinder from quitting on LinkageSpecDecls?

[plotfi]

Ah yeah it is, I reread your description. Can we add a test? Otherwise LGTM.

[zoecarver]

Yep added a test!

[zoecarver]

@swift-ci please smoke test