ci: fix llvm 19 + libstdc++ build by patching the g++ library

.github/patches/gcc_14_2.diff

@@ -0,0 +1,47 @@
+From c9e05b03c18e898be604ab90401476e9c473cc52 Mon Sep 17 00:00:00 2001
+From: Jonathan Wakely <[email protected]>
+Date: Thu, 16 May 2024 17:15:55 +0100
+Subject: [PATCH] libstdc++: Fix typo in _Grapheme_cluster_view::_Iterator
+ [PR115119]
+
+libstdc++-v3/ChangeLog:
+
+	PR libstdc++/115119
+	* include/bits/unicode.h (_Iterator::operator++(int)): Fix typo
+	in increment expression.
+	* testsuite/ext/unicode/grapheme_view.cc: Check post-increment
+	on view's iterator.
+
+	Source: https://gcc.gnu.org/git/?p=gcc.git;a=patch;h=c9e05b03c18e898be604ab90401476e9c473cc52
+	Modified paths, to make it work
+---
+ bits/unicode.h                 |  6 ++++--
+ 1 files changed, 4 insertions(+), 2 deletions(-)
+
+diff --git a/bits/unicode.h b/bits/unicode.h
+index 46238143fb61..a14a17c5dfcf 100644
+--- a/bits/unicode.h
++++ b/bits/unicode.h
+@@ -34,10 +34,12 @@
+ #include <array>
+ #include <bit>      // bit_width
+ #include <charconv> // __detail::__from_chars_alnum_to_val_table
++#include <string_view>
+ #include <cstdint>
+ #include <bits/stl_algo.h>
+ #include <bits/stl_iterator.h>
+-#include <bits/ranges_base.h>
++#include <bits/ranges_base.h> // iterator_t, sentinel_t, input_range, etc.
++#include <bits/ranges_util.h> // view_interface
+
+ namespace std _GLIBCXX_VISIBILITY(default)
+ {
+@@ -802,7 +804,7 @@ inline namespace __v15_1_0
+ 	operator++(int)
+ 	{
+ 	  auto __tmp = *this;
+-	  ++this;
++	  ++*this;
+ 	  return __tmp;
+ 	}
+

.github/workflows/build.yml

@@ -139,12 +139,11 @@ jobs:
           echo "CC=clang-19" >> "$GITHUB_ENV"
           echo "CXX=clang++-19" >> "$GITHUB_ENV"
           echo "OBJC=clang-19" >> "$GITHUB_ENV"
-          # Also install the newest g++ (For the libstd++ library)
-          echo "deb http://archive.ubuntu.com/ubuntu/ oracular main" | sudo tee -a /etc/apt/sources.list.d/new_ubuntu.list
-          sudo apt-get update
-          sudo apt-get install libstdc++-14-dev -y --no-install-recommends
-          sudo rm -rf /etc/apt/sources.list.d/new_ubuntu.list
-          sudo apt-get update
+          # Patch the libstd++ library, see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115119
+          # This is a dirty workaround, but it is needed, since gcc 14.2 (where this was patched usptream) is not easily available
+          # If we use the oracular (Ubuntu 24.10) repos, we could install gcc 14.2, but clang-19 isn't compatible with that
+          # TODO: remove this, after it works again
+          sudo patch -p1 /usr/include/c++/14/bits/unicode.h .github/patches/gcc_14_2.diff
 
       - name: Setup GCC (Linux)
         if: matrix.config.os == 'ubuntu' && matrix.config.use-clang == false