SIL Linker: Deserialize HiddenExternal functions

PublicNonABI function declarations deserialize as HiddenExternal,
then become SharedExternal after the body has been deserialized.
So try deserializing HiddenExternal too.

NFC until mandatory inlining is no longer eagerly deserializing.

Author: slavapestov

lib/SIL/Linker.cpp

@@ -55,7 +55,21 @@ void SILLinkerVisitor::maybeAddFunctionToWorklist(SILFunction *F) {
   if (!F->isExternalDeclaration())
     return;
 
-  if (isLinkAll() || hasSharedVisibility(F->getLinkage()))
+  // In the performance pipeline, we deserialize all reachable functions.
+  if (isLinkAll())
+    return addFunctionToWorklist(F);
+
+  // Otherwise, make sure to deserialize shared functions; we need to
+  // emit them into the client binary since they're not available
+  // externally.
+  if (hasSharedVisibility(F->getLinkage()))
+    return addFunctionToWorklist(F);
+
+  // Functions with PublicNonABI linkage are deserialized as having
+  // HiddenExternal linkage when they are declarations, then they
+  // become SharedExternal after the body has been deserialized.
+  // So try deserializing HiddenExternal functions too.
+  if (F->getLinkage() == SILLinkage::HiddenExternal)
     return addFunctionToWorklist(F);
 }