[flang][common] return ENUM_CLASS names definition to original state (llvm#143553)

This PR simply reverts a few lines in
bf60aa1 to their state in
bcba39a so that they are constant for
some of the build tests that require it. This should fix the breakage
caused by llvm#142022.

Author: akuhlens

flang/include/flang/Common/enum-class.h

@@ -62,14 +62,13 @@ constexpr std::array<std::string_view, ITEMS> EnumNames(const char *p) {
   enum class NAME { __VA_ARGS__ }; \
   [[maybe_unused]] static constexpr std::size_t NAME##_enumSize{ \
       ::Fortran::common::CountEnumNames(#__VA_ARGS__)}; \
-  [[maybe_unused]] static constexpr std::array<std::string_view, \
-      NAME##_enumSize> NAME##_names{ \
-      ::Fortran::common::EnumNames<NAME##_enumSize>(#__VA_ARGS__)}; \
   [[maybe_unused]] static inline std::size_t EnumToInt(NAME e) { \
     return static_cast<std::size_t>(e); \
   } \
   [[maybe_unused]] static inline std::string_view EnumToString(NAME e) { \
-    return NAME##_names[static_cast<std::size_t>(e)]; \
+    static const constexpr auto names{ \
+        ::Fortran::common::EnumNames<NAME##_enumSize>(#__VA_ARGS__)}; \
+    return names[static_cast<std::size_t>(e)]; \
   } \
   [[maybe_unused]] inline void ForEach##NAME(std::function<void(NAME)> f) { \
     for (std::size_t i{0}; i < NAME##_enumSize; ++i) { \