docker: Increase tmpfs size, print usage statistics at the end (#14)

At the time of writing, build of a recent LLVM commit inside an
ubuntu:25.10 container takes 1G under /opt/llvm-pauth and 4.7G
under /repo/build (or 1.3G and 5.2G, respectively, with assertions
enabled).

Author: atrosinenko

build.sh

@@ -106,7 +106,7 @@ build_in_docker() {
       --volume "$ROOT/src:$SRC_DIR:ro" \
       --volume "$ROOT/tmp:/tmp:rw" \
       --tmpfs "$DOCKER_BUILD_INSTALL_DIR:rw,exec,size=2G" \
-      --tmpfs "$BUILD_TMP:rw,exec,size=5G" \
+      --tmpfs "$BUILD_TMP:rw,exec,size=8G" \
       "$DOCKER_IMAGE_NAME" "$REPO_ROOT/scripts/build-in-docker.sh"
 }
 

scripts/build-in-docker.sh

@@ -12,6 +12,15 @@ export REPO_ROOT="$(pwd)/.."
 . ./global-vars
 export INSTALL_DIR="$DOCKER_BUILD_INSTALL_DIR"
 
+on_exit() {
+  # Print usage statistics for Docker volumes mounted into this container.
+  # Omit several unrelated mount points for readability.
+  df -h | grep -vE ' /(dev|etc|proc|sys)'
+}
+# Unconditionally print the statistics - whether the script terminates normally
+# or due to a subcommand error (as requested by "set -e").
+trap on_exit EXIT
+
 if ! ./build-all.sh; then
   echo "Containerized build failed - $BUILD_TMP is discarded automatically."
   exit 1