Avoid crashing if lldb imports C++ structs without enabling C++ interop.

Author: martinboehme

lib/ClangImporter/ImportDecl.cpp

@@ -3505,6 +3505,13 @@ namespace {
     }
 
     Decl *VisitCXXRecordDecl(const clang::CXXRecordDecl *decl) {
+      // lldb can call this without enabling C++ interop. To avoid crashing in
+      // Clang's Sema, fall back to importing this as a plain RecordDecl.
+      // FIXME: Fix lldb to enable C++ interop when appropriate, then remove
+      // this fallback.
+      if (!Impl.SwiftContext.LangOpts.EnableCXXInterop)
+        return VisitRecordDecl(decl);
+
       auto &clangSema = Impl.getClangSema();
       // Make Clang define the implicit default constructor if the class needs
       // it. Make sure we only do this if the class has been fully defined and