Function LLVMRustGlobalAddMetadata 

pub(crate) unsafe extern "C" fn LLVMRustGlobalAddMetadata<'a>(
    Val: &'a Value,
    KindID: MetadataKindId,
    Metadata: &'a Metadata,
)

FIXME: After dropping LLVM 21, migrate to LLVM-C’s LLVMGlobalAddMetadata.