[gcc r13-9070] c++: don't advertise C++20 concepts in C++14

[Jason Merrill via Gcc-cvs]

https://gcc.gnu.org/g:6ae9ef1b6bd77dca063b70a54fae46a397f6230a

commit r13-9070-g6ae9ef1b6bd77dca063b70a54fae46a397f6230a
Author: Jason Merrill <ja...@redhat.com>
Date:   Tue Oct 1 10:58:35 2024 -0400

    c++: don't advertise C++20 concepts in C++14
    
    There have been various problems with -std=c++14 -fconcepts; let's stop
    defining the feature test macro in that case.  And don't advertise Concepts
    TS support when it isn't enabled.
    
    gcc/c-family/ChangeLog:
    
            * c-cppbuiltin.cc (c_cpp_builtins): Don't define __cpp_concepts
            before C++17.

Diff:
---
 gcc/c-family/c-cppbuiltin.cc | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/gcc/c-family/c-cppbuiltin.cc b/gcc/c-family/c-cppbuiltin.cc
index 5d64625fcd7a..6983e9cebb60 100644
--- a/gcc/c-family/c-cppbuiltin.cc
+++ b/gcc/c-family/c-cppbuiltin.cc
@@ -1083,10 +1083,10 @@ c_cpp_builtins (cpp_reader *pfile)
        }
       if (flag_concepts)
         {
-         if (cxx_dialect >= cxx20)
-           cpp_define (pfile, "__cpp_concepts=202002L");
-          else
+         if (flag_concepts_ts && cxx_dialect < cxx20)
             cpp_define (pfile, "__cpp_concepts=201507L");
+         else if (cxx_dialect > cxx14)
+           cpp_define (pfile, "__cpp_concepts=202002L");
         }
       if (flag_contracts)
        {