[gcc r13-6807] libstdc++: Add comment to <format> (LWG 3720)

[Jonathan Wakely]

https://gcc.gnu.org/g:7d4f4ce6a5dcefc5c97a8d05461653cbf536b745

commit r13-6807-g7d4f4ce6a5dcefc5c97a8d05461653cbf536b745
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Mar 22 11:42:11 2023 +0000

    libstdc++: Add comment to <format> (LWG 3720)
    
    libstdc++-v3/ChangeLog:
    
            * include/std/format: Add a comment noting that the resolution
            of LWG 3720 has been applied..

Diff:
---
 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)