Function LLVMGetPreviousNamedMetadata 

pub unsafe extern "C" fn LLVMGetPreviousNamedMetadata(
    NamedMDNode: LLVMNamedMDNodeRef,
) -> LLVMNamedMDNodeRef

Decrement a NamedMDNode iterator to the previous NamedMDNode.

Returns NULL if the iterator was already at the beginning and there are no previous named metadata nodes.