add transition comment to ios_base::hexfloat (#3300)

Co-authored-by: Nicole Mazzuca <[email protected]>
Co-authored-by: Alex Guteniev <[email protected]>

Author: 3 people

stl/inc/xiosbase

@@ -44,7 +44,7 @@ public:
     static constexpr _Fmtflags scientific = static_cast<_Fmtflags>(0x1000);
     static constexpr _Fmtflags fixed      = static_cast<_Fmtflags>(0x2000);
 
-    static constexpr _Fmtflags hexfloat = static_cast<_Fmtflags>(0x3000); // added with TR1 (not in C++11)
+    static constexpr _Fmtflags hexfloat = static_cast<_Fmtflags>(0x3000); // TRANSITION, ABI, GH-3296
 
     static constexpr _Fmtflags boolalpha   = static_cast<_Fmtflags>(0x4000);
     static constexpr _Fmtflags _Stdio      = static_cast<_Fmtflags>(0x8000);
@@ -124,7 +124,7 @@ template <class _Dummy>
 const typename _Iosb<_Dummy>::_Fmtflags _Iosb<_Dummy>::fixed;
 
 template <class _Dummy>
-const typename _Iosb<_Dummy>::_Fmtflags _Iosb<_Dummy>::hexfloat; // added with TR1 (not in C++11)
+const typename _Iosb<_Dummy>::_Fmtflags _Iosb<_Dummy>::hexfloat; // TRANSITION, ABI, GH-3296
 
 template <class _Dummy>
 const typename _Iosb<_Dummy>::_Fmtflags _Iosb<_Dummy>::boolalpha;