fix(ci): honor APT mirrors in the prebuilt llama-cpp compile step

The builder-prebuilt path installs gcc-14 with apt directly and ignored
the APT_MIRROR/APT_PORTS_MIRROR build args the from-source path already
honors, so an ubuntu mirror outage broke every arm64 backend build. Pass
the args into the stage and run apt-mirror.sh (already in the build
context via COPY . /LocalAI) before the apt step.

Assisted-by: Claude:claude-fable-5
Signed-off-by: Richard Palethorpe <io@richiejp.com>

Author: richiejp

.docker/llama-cpp-compile.sh

@@ -28,6 +28,10 @@ if [ -z "${BUILD_TYPE:-}" ]; then
   # variants with it (the host never *selects* SME unless it has it, but every variant must
   # still compile).
   if [ "${TARGETARCH}" = "arm64" ]; then
+    # The prebuilt base inherits default ports.ubuntu.com sources; honor the
+    # APT_*_MIRROR build args here like the from-source path does, so this
+    # apt step survives a mirror outage.
+    sh /LocalAI/.docker/apt-mirror.sh || true
     apt-get update -qq && apt-get install -y -qq gcc-14 g++-14
     export CC=gcc-14 CXX=g++-14
   fi

backend/Dockerfile.llama-cpp

@@ -111,6 +111,10 @@ RUN make -BC /LocalAI/backend/cpp/llama-cpp package
 # ============================================================================
 FROM ${BUILDER_BASE_IMAGE} AS builder-prebuilt
 
+ARG APT_MIRROR
+ENV APT_MIRROR=${APT_MIRROR}
+ARG APT_PORTS_MIRROR
+ENV APT_PORTS_MIRROR=${APT_PORTS_MIRROR}
 ARG BUILD_TYPE
 ENV BUILD_TYPE=${BUILD_TYPE}
 ARG CUDA_DOCKER_ARCH