[gcc r13-6809] libstdc++: Add missing __cpp_lib_format macro to <version>

[Jonathan Wakely]

https://gcc.gnu.org/g:02e86035d30e9f7b8645ebb64f4028900fc37126

commit r13-6809-g02e86035d30e9f7b8645ebb64f4028900fc37126
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Mar 22 12:37:17 2023 +0000

    libstdc++: Add missing __cpp_lib_format macro to <version>
    
    libstdc++-v3/ChangeLog:
    
            * include/std/version (__cpp_lib_format): Define.
            * testsuite/std/format/functions/format.cc: Check it.

Diff:
---
 libstdc++-v3/include/std/version                      |  1 +
 libstdc++-v3/testsuite/std/format/functions/format.cc | 15 +++++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/libstdc++-v3/include/std/version b/libstdc++-v3/include/std/version
index 25ebfc3e512..a19c39c6cdd 100644
--- a/libstdc++-v3/include/std/version
+++ b/libstdc++-v3/include/std/version
@@ -277,6 +277,7 @@
 #define __cpp_lib_constexpr_utility 201811L
 #define __cpp_lib_constexpr_vector 201907L
 #define __cpp_lib_erase_if 202002L
+#define __cpp_lib_format 202106L
 #define __cpp_lib_generic_unordered_lookup 201811L
 #define __cpp_lib_interpolate 201902L
 #ifdef _GLIBCXX_HAS_GTHREADS
diff --git a/libstdc++-v3/testsuite/std/format/functions/format.cc b/libstdc++-v3/testsuite/std/format/functions/format.cc
index 7a155208a48..2a1b1560394 100644
--- a/libstdc++-v3/testsuite/std/format/functions/format.cc
+++ b/libstdc++-v3/testsuite/std/format/functions/format.cc
@@ -2,6 +2,21 @@
 // { dg-do run { target c++20 } }
 
 #include <format>
+
+#ifndef __cpp_lib_format
+# error "Feature test macro for std::format is missing in <format>"
+#elif __cpp_lib_format < 202106L
+# error "Feature test macro for std::format has wrong value in <format>"
+#endif
+
+#undef __cpp_lib_format
+#include <version>
+#ifndef __cpp_lib_format
+# error "Feature test macro for std::format is missing in <version>"
+#elif __cpp_lib_format < 202106L
+# error "Feature test macro for std::format has wrong value in <version>"
+#endif
+
 #include <string>
 #include <limits>
 #include <cstdint>