(*--... Operations on metadata .......,.....................................--*)
external mdstring : llcontext -> string -> llvalue = "llvm_mdstring"
external mdnode : llcontext -> llvalue array -> llvalue = "llvm_mdnode"
+external mdnull : llcontext -> llvalue = "llvm_mdnull"
external get_mdstring : llvalue -> string option = "llvm_get_mdstring"
external get_named_metadata : llmodule -> string -> llvalue array
= "llvm_get_namedmd"