CI: Add llvm-18 bin directory to GITHUB_PATH

Ensure that llvm-ar and other LLVM tools from version 18 are available
in the PATH during CI builds. Without this, only the versioned binaries
(e.g. llvm-ar-18) are found, which can cause build failures when
unversioned tool names are expected.

Author: visitorckw

.github/workflows/main.yml

@@ -52,6 +52,7 @@ jobs:
             wget https://apt.llvm.org/llvm.sh
             sudo chmod +x ./llvm.sh
             sudo ./llvm.sh 18
+            echo "/usr/lib/llvm-18/bin" >> $GITHUB_PATH
       shell: bash
     - name: Install compiler
       id: install_cc
@@ -313,6 +314,7 @@ jobs:
           wget https://apt.llvm.org/llvm.sh
           chmod +x ./llvm.sh
           ./llvm.sh 18
+          echo "/usr/lib/llvm-18/bin" >> $GITHUB_PATH
         # FIXME: gcc build fails on Aarch64/Linux hosts
         env: |
           CC: clang-18
@@ -342,6 +344,7 @@ jobs:
              brew install make dtc expect sdl2 sdl2_mixer bc e2fsprogs p7zip llvm@18 dcfldd
              .ci/riscv-toolchain-install.sh
              echo "${{ github.workspace }}/toolchain/bin" >> $GITHUB_PATH
+             echo "$(brew --prefix llvm@18)/bin" >> $GITHUB_PATH
      - name: Install compiler
        id: install_cc
        uses: rlalik/setup-cpp-compiler@master