From 5f9b983798042038e5b86bc9265bab75c7cfb4e8 Mon Sep 17 00:00:00 2001
From: jzmaddock <john@johnmaddock.co.uk>
Date: Fri, 5 Mar 2021 12:05:31 +0000
Subject: [PATCH] Fix up libstdc++3 for older clang with a newer std lib.

---
 include/boost/config/stdlib/libstdcpp3.hpp | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/include/boost/config/stdlib/libstdcpp3.hpp b/include/boost/config/stdlib/libstdcpp3.hpp
index 163c4a7f..24126192 100644
--- a/include/boost/config/stdlib/libstdcpp3.hpp
+++ b/include/boost/config/stdlib/libstdcpp3.hpp
@@ -362,6 +362,18 @@ extern "C" char *gets (char *__s);
 #  define BOOST_NO_CXX20_HDR_COROUTINE
 #endif
 
+//
+// These next defines are mostly for older clang versions with a newer libstdc++ :
+//
+#if !defined(__cpp_lib_concepts)
+#if !defined(BOOST_NO_CXX20_HDR_COMPARE)
+#  define BOOST_NO_CXX20_HDR_COMPARE
+#endif
+#if !defined(BOOST_NO_CXX20_HDR_CONCEPTS)
+#  define BOOST_NO_CXX20_HDR_CONCEPTS
+#endif
+#endif
+
 //
 // Headers not present on Solaris with the Oracle compiler:
 #if defined(__SUNPRO_CC) && (__SUNPRO_CC < 0x5140)