[gcmole] Make packaging more deterministic

Tar and Gzip would include timestamps for files in the gcmole package,
which meant that they weren't deterministic across multiple builds. Now
we strip out the timestamps (as well as owner/group information) to make
the packaging more deterministic.

Change-Id: Iec3195ede4150c1603927fec748455329a8da677
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3245112Reviewed-by: Liviu Rau <liviurau@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77539}

tools/gcmole/package.sh

@@ -33,9 +33,17 @@ mkdir -p "${PACKAGE_DIR}/lib"
 cp -r "${BUILD_DIR}/lib/clang" "${PACKAGE_DIR}/lib"
 cp "${THIS_DIR}/libgcmole.so" "${PACKAGE_DIR}"
 
-# Generate the archive
+# Generate the archive. Set some flags on tar to make the output more
+# deterministic (e.g. not dependent on timestamps by using the timestamp of
+# gcmole.cc for all files)
 cd "$(dirname "${PACKAGE_DIR}")"
-tar -c -z -f "${PACKAGE_FILE}" "$(basename "${PACKAGE_DIR}")"
+tar \
+  --sort=name \
+  --owner=root:0 \
+  --group=root:0 \
+  --mtime="${THIS_DIR}/gcmole.cc" \
+  --create \
+  "$(basename "${PACKAGE_DIR}")" | gzip --no-name >"${PACKAGE_FILE}"
 
 # Generate checksum
 sha1sum "${PACKAGE_FILE}" | awk '{print $1}' > "${PACKAGE_SUM}"