ci: add clang++-18 to ubuntu 22.04

.github/docker/ubuntu22.04/c4core-install

@@ -24,6 +24,7 @@ case $what in
         $script gcc-14
         ;;
     clang-all)
+        $script clang-18
         $script clang-17
         $script clang-16
         $script clang-15
@@ -261,6 +262,18 @@ case $what in
         apt-get install -y \
                 clang-17 clang-tidy-17
         ;;
+    clang++-18|clang-18)
+        apt-get update
+        apt-get install -y \
+                wget \
+                software-properties-common
+        wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key 2>/dev/null | apt-key add -
+        apt-add-repository --yes --no-update ppa:ubuntu-toolchain-r/test
+        apt-add-repository --yes --no-update "deb http://apt.llvm.org/jammy/ llvm-toolchain-jammy-18 main"
+        apt-get update
+        apt-get install -y \
+                clang-18 clang-tidy-18
+        ;;
     arm-none-eabi)
         # taken from: https://askubuntu.com/questions/1243252/how-to-install-arm-none-eabi-gdb-on-ubuntu-20-04-lts-focal-fossa/1371525#1371525
         apt-get update