Out of scope.Luau::CodeGen::compileInternal generates and installs
native machine code; luaur’s execution oracle is the bytecode interpreter
(see docs/CONFORMANCE.md), so this was never ported. It survived only as an
extern declaration of the original C++ mangled symbol, which has no
implementation to link against (lld DCE’d the reference on Linux/macOS, MSVC
kept it → unresolved external symbol on Windows). Stub it explicitly.