unwind: disable RTTI during the build of libunwind Disable the type information emission for libunwind. libunwind does not use `dynamic_cast`. This results in a smaller binary, and more importantly, avoids the dependency on libc++abi. This ensures that we have complete symbol resolution of symbols on ELF targets without linking to the C++ runtime support library. This change avoids the emission of a reference to `__si_class_type_info`.