[PATCH v2] libstdc++: Use __promote_3 for std::hypot [PR121097]

[Jonathan Wakely]

The __promoted_t alias is only defined when __cpp_fold_expressions is
defined, which might not be the case for some hypothetical C++17
compilers.

Change the 3-arg std::hypot to just use __gnu_cxx::__promote_3 which is
always available.

libstdc++-v3/ChangeLog:

        PR libstdc++/121097
        * include/c_global/cmath (hypot): Use __promote_3 instead of
        __promoted.
---

Patch v2 just uses Tomasz's suggestion to use __promote_3 in std:hypot,
which is much simpler than adding a fallback definition of __promoted_t.

Tested x86_64-linux.

 libstdc++-v3/include/c_global/cmath | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/include/c_global/cmath 
b/libstdc++-v3/include/c_global/cmath
index 27c21ca19eb6..65a3b8144f35 100644
--- a/libstdc++-v3/include/c_global/cmath
+++ b/libstdc++-v3/include/c_global/cmath
@@ -3792,10 +3792,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   { return std::__hypot3<long double>(__x, __y, __z); }
 
   template<typename _Tp, typename _Up, typename _Vp>
-    __gnu_cxx::__promoted_t<_Tp, _Up, _Vp>
+    typename __gnu_cxx::__promote_3<_Tp, _Up, _Vp>::__type
     hypot(_Tp __x, _Up __y, _Vp __z)
     {
-      using __type = __gnu_cxx::__promoted_t<_Tp, _Up, _Vp>;
+      using __type = typename __gnu_cxx::__promote_3<_Tp, _Up, _Vp>::__type;
       return std::__hypot3<__type>(__x, __y, __z);
     }
 
-- 
2.50.1