libstdc++: Workaround for missing 'using enum' in Clang 12

Once we no longer care about older compilers without this feature, we
can drop these static data members, so the names don't have to be
visible at class scope.

libstdc++-v3/ChangeLog:

	* libsupc++/compare (_Strong_order) [!__cpp_using_enum]: Add
	static data members for _Fp_fmt enumerators.

diff --git a/libstdc++-v3/libsupc++/compare b/libstdc++-v3/libsupc++/compare
index 6e1ed53..e9cf913 100644 (file)
--- a/libstdc++-v3/libsupc++/compare
+++ b/libstdc++-v3/libsupc++/compare
@@ -677,12 +677,25 @@ namespace std
        // TODO: _Bfloat16,
       };
 
+#ifndef __cpp_using_enum
+      // XXX Remove these once 'using enum' support is ubiquitous.
+      static constexpr _Fp_fmt _Binary16 = _Fp_fmt::_Binary16;
+      static constexpr _Fp_fmt _Binary32 = _Fp_fmt::_Binary32;
+      static constexpr _Fp_fmt _Binary64 = _Fp_fmt::_Binary64;
+      static constexpr _Fp_fmt _Binary128 = _Fp_fmt::_Binary128;
+      static constexpr _Fp_fmt _X86_80bit = _Fp_fmt::_X86_80bit;
+      static constexpr _Fp_fmt _M68k_80bit = _Fp_fmt::_M68k_80bit;
+      static constexpr _Fp_fmt _Dbldbl = _Fp_fmt::_Dbldbl;
+#endif
+
       // Identify the format used by a floating-point type.
       template<typename _Tp>
        static consteval _Fp_fmt
        _S_fp_fmt() noexcept
        {
+#ifdef __cpp_using_enum
          using enum _Fp_fmt;
+#endif
 
          // Identify these formats first, then assume anything else is IEEE.
          // N.B. ARM __fp16 alternative format can be handled as binary16.
@@ -810,7 +823,9 @@ namespace std
            return __builtin_bit_cast(int16_t, __val);
          else
            {
+#ifdef __cpp_using_enum
              using enum _Fp_fmt;
+#endif
              constexpr auto __fmt = _S_fp_fmt<_Tp>();
              if constexpr (__fmt == _X86_80bit || __fmt == _M68k_80bit)
                {
@@ -862,7 +877,9 @@ namespace std
          if (__ix == __iy)
            return strong_ordering::equal; // All bits are equal, we're done.
 
+#ifdef __cpp_using_enum
          using enum _Fp_fmt;
+#endif
          constexpr auto __fmt = _S_fp_fmt<_Tp>();
 
          if constexpr (__fmt == _Dbldbl) // double-double