Revert "[cxx-interop] Do not look into extern blocks in libc++'s std_private_random_binomial_distribution"

This reverts commit 8e71509.

Author: egorzhdan

lib/ClangImporter/SwiftLookupTable.cpp

@@ -2046,17 +2046,7 @@ void importer::addEntryToLookupTable(SwiftLookupTable &table,
                   addDeclsFromContext(nestedLinkageSpecDecl);
               }
             };
-
-        // HACK: libc++ redeclares lgamma_r in one of its headers, and that
-        // declaration hijacks lgamma_r from math.h where it is originally
-        // defined. This causes deserialization issues when loading the Darwin
-        // overlay on Apple platforms, because Swift cannot find lgamma_r in
-        // module _math.
-        bool shouldSkip = canonicalMember->getOwningModule() &&
-                          canonicalMember->getOwningModule()->Name ==
-                              "std_private_random_binomial_distribution";
-        if (!shouldSkip)
-          addDeclsFromContext(linkageSpecDecl);
+        addDeclsFromContext(linkageSpecDecl);
       }
     }
   }