AddNamedMetadata fails for strings in the C interface

[demoitem]

Calling this via the C interface

LLVMAddNamedMetadataOperand(M, "llvm.ident",
LLVMMetadataAsValue(LLVMGetModuleContext(M),
LLVMMDStringInContext2(LLVMGetModuleContext(M), "foo", 3)));

produces an assert

Core.cpp:1094: llvm::MDNode* extractMDNode(llvm::MetadataAsValue*): Assertion `(isa(MD) || isa(MD)) && "Expected a metadata node or a canonicalized constant"' failed.