The extern "C" functions exported with MLIR_ASYNCRUNTIME_EXPORT are inside namespace mlir::runtime. MSVC has problems in associating the decls with the impls if they are not qualified properly.
This patch put the impls inside the mlir::runtime namespace as the decls.
Maybe add a comment that it violates https://llvm.org/docs/CodingStandards.html#use-namespace-qualifiers-to-implement-previously-declared-functions for a reason?