LibSMI is used for MIB and PIB parsing and for OID resolution.
If this library isn’t already installed or available as a package for your platform, you can get it at https://www.ibr.cs.tu-bs.de/projects/libsmi/.
Wireshark uses the source libSMI distribution at https://www.ibr.cs.tu-bs.de/projects/libsmi/. LibSMI is cross-compiled using MinGW32. It’s stored in the libsmi zip archives at https://dev-libs.wireshark.org/windows/packages/.