Fix MLIR build after header change in LLVM (NFC)

Author: Mehdi Amini

mlir/lib/ExecutionEngine/ExecutionEngine.cpp

@@ -30,6 +30,7 @@
 #include "llvm/IR/IRBuilder.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/Error.h"
+#include "llvm/Support/Host.h"
 #include "llvm/Support/TargetRegistry.h"
 #include "llvm/Support/ToolOutputFile.h"