ci: Test building sysroots with LLVM

Add --llvm argument to the container_test.sh script. Use it on CI in
combination with the llvm stage3 image.

Signed-off-by: Michal Rostecki <vadorovsky@protonmail.com>

Author: vadorovsky

.github/workflows/crossdev.yml

@@ -100,19 +100,36 @@ jobs:
           - target: bpf-unknown-none
             args: --skip-system
         stage3:
-          - latest # `openrc` (glibc+GCC) is tagged as `latest`
-          - musl
+          - latest # glibc+GCC
+          - llvm # glibc+LLVM and GCC as a fallback
+          - musl # musl+GCC
       fail-fast: false
     name: crossdev target=${{ matrix.target.target }} stage3=${{ matrix.stage3 }}
+    env:
+      CONTAINER_ENGINE: docker
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
 
-      - name: Create cross environment
-        env:
-          CONTAINER_ENGINE: docker
+      - name: Create cross environment with GCC
+        # Building GCC-based sysroots on llvm stage3 should be possible, since
+        # it contains a fallback GCC toolchain. But in practice, it fails for
+        # certain architectures. Pull requests welcome!
+        if: ${{ !contains(matrix.stage3, 'llvm') }}
         run: |
           ./scripts/container_test.sh \
             --tag ${{ matrix.stage3 }} \
             --target ${{ matrix.target.target }} \
             ${{ matrix.target.args }}
+
+      - name: Create cross environment with LLVM
+        # * We need LLVM toolchain to be present in the stage3.
+        # * Building sysroots with glibc and LLVM is not yet supported.
+        # * musleabi targets don't work - pull requests welcome!
+        if: ${{ contains(matrix.stage3, 'llvm') && endsWith(matrix.target.target, 'musl') }}
+        run: |
+          ./scripts/container_test.sh \
+            --llvm \
+            --tag ${{ matrix.stage3 }} \
+            --target ${{ matrix.target.target }} \
+            ${{ matrix.target.args }}

scripts/container_test.sh

@@ -6,6 +6,7 @@ print_help() {
 	echo "Usage: $0 [OPTIONS]
 
 Options:
+  --llvm                Use LLVM/Clang as a cross compiler
   --skip-system         Skip emerging the @system set after setting up crossdev.
   --tag <tag>           Specify the container tag to use. Default is 'latest'.
   --target <target>     Specify the target architecture for crossdev. Required.
@@ -54,6 +55,7 @@ CONTAINER_NAME=${CONTAINER_NAME:-"crossdev"}
 CONTAINER_URI=${CONTAINER_URI:-"docker.io/gentoo/stage3"}
 CONTAINER_TAG="latest"
 EMERGE_SYSTEM=1
+USE_LLVM=0
 TOPDIR=$(git rev-parse --show-toplevel)
 
 remove_container || true
@@ -65,6 +67,10 @@ while [[ $# -gt 0 ]]; do
 			print_help
 			exit 0
 			;;
+		--llvm)
+			USE_LLVM=1
+			shift 1
+			;;
 		--skip-system)
 			EMERGE_SYSTEM=0
 			shift 1