[gcc r15-8933] libstdc++: do not advertise full P2562R1 support

[Giuseppe D'Angelo]

https://gcc.gnu.org/g:a264c270fde292678893493fec0d0dd01ee5c4ec

commit r15-8933-ga264c270fde292678893493fec0d0dd01ee5c4ec
Author: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
Date:   Wed Mar 26 15:30:47 2025 +0100

    libstdc++: do not advertise full P2562R1 support
    
    P2562R1 ("constexpr Stable Sorting") adds constexpr to stable_sort,
    stable_partition and inplace_merge. However only the first is already
    implemented in libstdc++, so we shouldn't bump the feature-testing
    macro to the bumped C++26 value. This commit sets it to one less
    than the final value.
    
    Amends r15-7708-gff43f9853d3b10.
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/version.def (constexpr_algorithms): Change
            the value of the feature-testing macro.
            * include/bits/version.h: Regenerate.
            * testsuite/25_algorithms/cpp_lib_constexpr.cc: Amend the
            check of the feature-testing macro.

Diff:
---
 libstdc++-v3/include/bits/version.def                     | 2 +-
 libstdc++-v3/include/bits/version.h                       | 4 ++--
 libstdc++-v3/testsuite/25_algorithms/cpp_lib_constexpr.cc | 2 +-
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/libstdc++-v3/include/bits/version.def b/libstdc++-v3/include/bits/version.def
index 1468c0491b71..7ef60af39deb 100644
--- a/libstdc++-v3/include/bits/version.def
+++ b/libstdc++-v3/include/bits/version.def
@@ -1117,7 +1117,7 @@ ftms = {
 ftms = {
   name = constexpr_algorithms;
   values = {
-    v = 202306;
+    v = 202305;
     cxxmin = 26;
   };
   values = {
diff --git a/libstdc++-v3/include/bits/version.h b/libstdc++-v3/include/bits/version.h
index f7c9849893da..a96ff49efa41 100644
--- a/libstdc++-v3/include/bits/version.h
+++ b/libstdc++-v3/include/bits/version.h
@@ -1257,9 +1257,9 @@
 
 #if !defined(__cpp_lib_constexpr_algorithms)
 # if (__cplusplus >  202302L)
-#  define __glibcxx_constexpr_algorithms 202306L
+#  define __glibcxx_constexpr_algorithms 202305L
 #  if defined(__glibcxx_want_all) || defined(__glibcxx_want_constexpr_algorithms)
-#   define __cpp_lib_constexpr_algorithms 202306L
+#   define __cpp_lib_constexpr_algorithms 202305L
 #  endif
 # elif (__cplusplus >= 202002L)
 #  define __glibcxx_constexpr_algorithms 201806L
diff --git a/libstdc++-v3/testsuite/25_algorithms/cpp_lib_constexpr.cc b/libstdc++-v3/testsuite/25_algorithms/cpp_lib_constexpr.cc
index 3f60e9961158..3e5e55252fca 100644
--- a/libstdc++-v3/testsuite/25_algorithms/cpp_lib_constexpr.cc
+++ b/libstdc++-v3/testsuite/25_algorithms/cpp_lib_constexpr.cc
@@ -23,7 +23,7 @@
 #ifndef __cpp_lib_constexpr_algorithms
 # error "Feature-test macro for constexpr algorithms missing"
 #elif __cplusplus > 202302L
-# if __cpp_lib_constexpr_algorithms < 202306L
+# if __cpp_lib_constexpr_algorithms < 202305L
 #  error "Feature-test macro for constexpr algorithms has wrong value"
 # endif
 #elif __cpp_lib_constexpr_algorithms < 201806L