From 96c2dacf44fa26ccdfe253d0bc15331766956ace Mon Sep 17 00:00:00 2001
From: Efraim Flashner <efraim@flashner.co.il>
Date: Tue, 17 Dec 2024 09:24:12 +0200
Subject: [PATCH] gnu: gcc-muslboot: Backport c++ builtin values.

* gnu/packages/commencement.scm (gcc-muslboot)[arguments]: Add a custom
phase backporting the correct definitions for __cplusplus.

Change-Id: I64a77dc4d4cb5936e650d37585145f171adc8572
---
 gnu/packages/commencement.scm | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/gnu/packages/commencement.scm b/gnu/packages/commencement.scm
index 4f52b199c2..f0eedca5f8 100644
--- a/gnu/packages/commencement.scm
+++ b/gnu/packages/commencement.scm
@@ -2031,6 +2031,19 @@ ac_cv_c_float_format='IEEE (little-endian)'
                  #$configure-flags))))
        ((#:phases phases)
         #~(modify-phases #$phases
+            (add-after 'unpack 'adjust-builtin-cplusplus-variable
+              (lambda _
+                ;; These values are backported from later releases of GCC.
+                ;; See gcc commit 1fb80b0c5359f696aa61d537e25b7901d8b56ff7.
+                (substitute* "libcpp/init.c"
+                  (("_cpp_define_builtin \\(pfile, \"__cplusplus 1\"\\);")
+                   (string-append "{
+      if (CPP_OPTION (pfile, lang) == CLK_CXX0X
+       || CPP_OPTION (pfile, lang) == CLK_GNUCXX0X)
+       _cpp_define_builtin (pfile, \"__cplusplus 201103L\");
+      else
+       _cpp_define_builtin (pfile, \"__cplusplus 199711L\");
+    }")))))
             (add-after 'apply-riscv64-patch 'apply-second-riscv64-patch
               (lambda* (#:key inputs #:allow-other-keys)
                 (let ((patch-file