[committed] libstdc++: Add comment to (LWG 3720)

[Jonathan Wakely via Gcc-patches]

Tested powerpc64le-linux, pushed to trunk.

-- >8--

libstdc++-v3/ChangeLog:

        * include/std/format: Add a comment noting that the resolution
        of LWG 3720 has been applied..
---
 libstdc++-v3/include/std/format | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/libstdc++-v3/include/std/format b/libstdc++-v3/include/std/format
index b1e627048de..0e40bce5c15 100644
--- a/libstdc++-v3/include/std/format
+++ b/libstdc++-v3/include/std/format
@@ -3119,6 +3119,8 @@ namespace __format
        // 3721. Allow an arg-id with a value of zero for width
        else if constexpr (sizeof(_Tp) <= sizeof(long long))
          {
+           // _GLIBCXX_RESOLVE_LIB_DEFECTS
+           // 3720. Restrict the valid types of arg-id for width and precision
            if constexpr (__is_unsigned_integer<_Tp>::value)
              return __arg;
            else if constexpr (__is_signed_integer<_Tp>::value)
-- 
2.39.2