ci: add cross-build headers for Linux arm64 kernel builds

Include the common cross-build compatibility headers alongside Clang's resource headers for the Ubuntu aarch64 buildkernel path so genoffset can resolve sys/cdefs.h.

AI-Assisted-by: OpenAI Codex (GPT-5)
Signed-off-by: Lucas Holt <luke@foolishgames.com>

Author: laffer1

.github/workflows/cross-bootstrap-tools.yml

@@ -69,6 +69,6 @@ jobs:
           args+=(TARGET=${{ matrix.target }} TARGET_ARCH=${{ matrix.target_arch }} KERNCONF=GENERIC NO_MODULES=yes buildkernel -s -j"$NPROC")
           if [ "${{ runner.os }}" = "Linux" ] && [ "${{ matrix.target_arch }}" = "aarch64" ]; then
             resource_dir=$(/usr/lib/llvm-18/bin/clang -print-resource-dir)
-            args+=("KERNEL_FLAGS=CFLAGS+=-idirafter ${resource_dir}/include")
+            args+=("KERNEL_FLAGS=CFLAGS+=-idirafter ${PWD}/tools/build/cross-build/include/common CFLAGS+=-idirafter ${resource_dir}/include")
           fi
           "${args[@]}"