[gcc(refs/users/mikael/heads/pr121185_v01)] libstdc++: Ensure std::make_unsigned<Enum> works for 128-bit enum

[Mikael Morin]

https://gcc.gnu.org/g:3f82cfc2feac2edcea0052c7541f48f3ee43854e

commit 3f82cfc2feac2edcea0052c7541f48f3ee43854e
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Sun Jul 13 15:05:52 2025 +0100

    libstdc++: Ensure std::make_unsigned<Enum> works for 128-bit enum
    
    Another follow-up to r16-2190-g4faa42ac0dee2c, ensuring that make_signed
    and make_unsigned work on enumeration types with 128-bit integers as
    their underlying type.
    
    libstdc++-v3/ChangeLog:
    
            * include/std/type_traits (__make_unsigned_selector): Add
            unsigned __int128 to type list.
            * testsuite/20_util/make_unsigned/int128.cc: New test.
    
    Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>

Diff:
---
 libstdc++-v3/include/std/type_traits                   |  7 ++++++-
 libstdc++-v3/testsuite/20_util/make_unsigned/int128.cc | 14 ++++++++++++++
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
index 78a5ee8c0eb4..ff23544fbf03 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -1992,8 +1992,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     : __make_unsigned_selector_base
     {
       // With -fshort-enums, an enum may be as small as a char.
+      __extension__
       using _UInts = _List<unsigned char, unsigned short, unsigned int,
-			   unsigned long, unsigned long long>;
+			   unsigned long, unsigned long long
+#ifdef __SIZEOF_INT128__
+			   , unsigned __int128
+#endif
+			  >;
 
       using __unsigned_type = typename __select<sizeof(_Tp), _UInts>::__type;
 
diff --git a/libstdc++-v3/testsuite/20_util/make_unsigned/int128.cc b/libstdc++-v3/testsuite/20_util/make_unsigned/int128.cc
new file mode 100644
index 000000000000..46c07b7669e5
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/make_unsigned/int128.cc
@@ -0,0 +1,14 @@
+// { dg-do compile { target c++11 } }
+// { dg-add-options strict_std }
+
+#include <type_traits>
+
+#ifdef __SIZEOF_INT128__
+enum E : __int128 { };
+using U = std::make_unsigned<E>::type;
+static_assert( std::is_integral<U>::value, "type is an integer" );
+static_assert( sizeof(U) == sizeof(E), "width of type is 128 bits" );
+using I = std::make_signed<E>::type;
+static_assert( std::is_integral<I>::value, "type is an integer" );
+static_assert( sizeof(I) == sizeof(E), "width of type is 128 bits" );
+#endif