Index: flang/include/flang/Common/idioms.h
===================================================================
--- flang/include/flang/Common/idioms.h
+++ flang/include/flang/Common/idioms.h
@@ -20,6 +20,7 @@
 #include <tuple>
 #include <type_traits>
 #include <variant>
+#include "llvm/Support/Compiler.h"
 
 #if __GNUC__ == 7
 // Avoid a deduction bug in GNU 7.x headers by forcing the answer.
@@ -98,10 +99,6 @@
   } \
   template <typename A> constexpr bool T{class_trait_ns_##T::trait_value<A>()};
 
-#if !defined ATTRIBUTE_UNUSED && (__clang__ || __GNUC__)
-#define ATTRIBUTE_UNUSED __attribute__((unused))
-#endif
-
 // Define enum class NAME with the given enumerators, a static
 // function EnumToString() that maps enumerators to std::string,
 // and a constant NAME_enumSize that captures the number of items
@@ -116,11 +113,11 @@
 
 #define ENUM_CLASS(NAME, ...) \
   enum class NAME { __VA_ARGS__ }; \
-  ATTRIBUTE_UNUSED static constexpr std::size_t NAME##_enumSize{[] { \
+  LLVM_ATTRIBUTE_UNUSED static constexpr std::size_t NAME##_enumSize{[] { \
     enum { __VA_ARGS__ }; \
     return Fortran::common::ListItemCount{__VA_ARGS__}.value; \
   }()}; \
-  ATTRIBUTE_UNUSED static inline std::string EnumToString(NAME e) { \
+  LLVM_ATTRIBUTE_UNUSED static inline std::string EnumToString(NAME e) { \
     return Fortran::common::EnumIndexToString( \
         static_cast<int>(e), #__VA_ARGS__); \
   }