[flang] Add runtime interface for COMMAND_ARGUMENT_COUNT

Differential Revision: https://reviews.llvm.org/D108687

Author: rovka

flang/runtime/command.h

@@ -0,0 +1,25 @@
+//===-- runtime/command.h ---------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef FORTRAN_RUNTIME_COMMAND_H_
+#define FORTRAN_RUNTIME_COMMAND_H_
+
+#include "cpp-type.h"
+#include "entry-names.h"
+
+namespace Fortran::runtime {
+extern "C" {
+// 16.9.51 COMMAND_ARGUMENT_COUNT
+//
+// Lowering may need to cast the result to match the precision of the default
+// integer kind.
+CppTypeFor<TypeCategory::Integer, 4> RTNAME(ArgumentCount)();
+}
+} // namespace Fortran::runtime
+
+#endif // FORTRAN_RUNTIME_COMMAND_H_