Add info about the "testing only" aspect of --allow-unregistered-dialect in the cl::opt desc (NFC)

Author: joker-eph

mlir/lib/Tools/mlir-opt/MlirOptMain.cpp

@@ -240,7 +240,7 @@ LogicalResult mlir::MlirOptMain(int argc, char **argv, llvm::StringRef toolName,
 
   static cl::opt<bool> allowUnregisteredDialects(
       "allow-unregistered-dialect",
-      cl::desc("Allow operation with no registered dialects"), cl::init(false));
+      cl::desc("Allow operation with no registered dialects (discouraged: testing only!)"), cl::init(false));
 
   static cl::opt<bool> showDialects(
       "show-dialects", cl::desc("Print the list of registered dialects"),

mlir/lib/Tools/mlir-translate/MlirTranslateMain.cpp

@@ -39,7 +39,7 @@ LogicalResult mlir::mlirTranslateMain(int argc, char **argv,
 
   static llvm::cl::opt<bool> allowUnregisteredDialects(
       "allow-unregistered-dialect",
-      llvm::cl::desc("Allow operation with no registered dialects"),
+      llvm::cl::desc("Allow operation with no registered dialects (discouraged: testing only!)"),
       llvm::cl::init(false));
 
   static llvm::cl::opt<bool> splitInputFile(