From 66e18dd329f4728409abced4138562a079b30ccd Mon Sep 17 00:00:00 2001
From: Sam James <sam@gentoo.org>
Date: Sat, 12 Apr 2025 16:43:49 +0100
Subject: [PATCH] toolchain-funcs.eclass: update tc-get-cxx-stdlib for C++20

<ciso646> is gone from C++20, so use <version> for >= C++20.

See https://stackoverflow.com/a/31658120.

Signed-off-by: Sam James <sam@gentoo.org>
---
 eclass/toolchain-funcs.eclass | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/eclass/toolchain-funcs.eclass b/eclass/toolchain-funcs.eclass
index ae21a18a14c23..baf032bbd4ecc 100644
--- a/eclass/toolchain-funcs.eclass
+++ b/eclass/toolchain-funcs.eclass
@@ -1156,7 +1156,12 @@ tc-enables-ssp-all() {
 #
 # If the library is not recognized, the function returns 1.
 tc-get-cxx-stdlib() {
-	local code='#include <ciso646>
+	local code='
+#if __cplusplus >= 202002L
+	#include <version>
+#else
+	#include <ciso646>
+#endif
 
 #if defined(_LIBCPP_VERSION)
 	HAVE_LIBCXX