EISW-173753 Fix invalid TableGen flag in LLVM 20.x causing precommit failure

Also adds explicit registration for the CMake/TableGen-passed flag in mlir-src-sharder after command line reset.

Author: sramasit

llvm/cmake/modules/TableGen.cmake

@@ -81,7 +81,7 @@ function(tablegen project ofn)
   endif()
 
   if (NOT LLVM_ENABLE_WARNINGS)
-    list(APPEND LLVM_TABLEGEN_FLAGS "-Dno-warn-on-unused-template-args")
+    list(APPEND LLVM_TABLEGEN_FLAGS "--no-warn-on-unused-template-args")
   endif()
 
   # We need both _TABLEGEN_TARGET and _TABLEGEN_EXE in the  DEPENDS list

mlir/tools/mlir-src-sharder/mlir-src-sharder.cpp

@@ -72,6 +72,14 @@ int main(int argc, char **argv) {
           "Name of the macro to be defined -- ignored by mlir-src-sharder"),
       llvm::cl::value_desc("macro name"), llvm::cl::Prefix);
 
+  // CMake/TableGen pass this flag, re-registering after ResetCommandLineParser
+  // avoids "unknown argument" errors.
+  // TODO: Investigate if mlir-src-sharder's argument parsing can be
+  // aligned with generic tablegen options more broadly.
+  llvm::cl::opt<bool> noWarnOnUnusedTemplateArg(
+      "no-warn-on-unused-template-args",
+      llvm::cl::desc("Disable unused template argument warnings."));
+
   llvm::InitLLVM y(argc, argv);
   llvm::cl::ParseCommandLineOptions(argc, argv);