Jitter entropy import script (#2224)

Prepare being able to do a clean Jitter Entropy import from upstream. This creates a script that can do the import.
No source code has been imported yet.

third_party/jitterentropy/import.sh

@@ -0,0 +1,80 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+# Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+# SPDX-License-Identifier: Apache-2.0 OR ISC
+
+# https://github.com/smuellerDD/jitterentropy-library -> AWS-LC importer script
+#
+# This script imports a version of Jitter Entropy source into AWS-LC.
+#
+# Usage:
+#
+# ```
+# rm -rf ./jitterentropy-library
+# ./import.sh
+# ```
+#
+# This imports Jitter Entropy from https://github.com/smuellerDD/jitterentropy-library
+# and leaves import meta data in META.yml.
+#
+# If you want to import a specific branch/tag or from a specific repository
+# either set GITHUB_TARGET or GITHUB_REPOSITORY as below:
+#
+# ```
+# GITHUB_REPOSITORY=<repo owner>/<repo name> GITHUB_TARGET=<branch or tag> ./import.sh
+# ```
+
+GITHUB_SERVER_URL="https://github.com/"
+GITHUB_REPOSITORY=${GITHUB_REPOSITORY:=smuellerDD/jitterentropy-library.git}
+GITHUB_TARGET=${GITHUB_TARGET:=master}
+
+SRC="jitterentropy-library"
+TMP="TEMP_CAN_DELETE"
+
+# Check if TMP directory already exists
+if [ -d "${TMP}" ]; then
+    echo "Source directory or symlink ${TMP} does already exist -- please remove it before re-running the importer"
+    exit 1
+fi
+
+# Check if source directory already exists
+if [ -d "${SRC}" ]; then
+    echo "Source directory or symlink ${SRC} does already exist -- please remove it before re-running the importer"
+    exit 1
+fi
+
+mkdir ${TMP}
+
+echo "Fetching repository ..."
+git clone ${GITHUB_SERVER_URL}/${GITHUB_REPOSITORY} ${TMP} --branch ${GITHUB_TARGET} --single-branch > /dev/null
+GITHUB_COMMIT=$(cd ${TMP} >/dev/null; git rev-parse HEAD)
+
+echo "Copy source code ..."
+mkdir ${SRC}
+cp -rH ${TMP}/* ${SRC}
+
+echo "Remove temporary artifacts ..."
+rm -rf ${TMP}
+
+echo "Remove upstream repository build scripts to avoid them being invoked ..."
+rm "${SRC}/CMakeLists.txt"
+rm "${SRC}/Makefile"
+
+echo "Generating META.yml file ..."
+cat <<EOF > META.yml
+name: ${SRC}
+source: ${GITHUB_REPOSITORY}
+commit: ${GITHUB_COMMIT}
+target: ${GITHUB_TARGET}
+imported-at: $(env TZ=UTC date "+%Y-%m-%dT%H:%M:%S%z")
+EOF
+
+# Submodule path might be cached.
+echo ""
+echo "Post actions: Run"
+echo "$ git add jitterentropy-library ; git commit -m \"Imported Jitter Entropy version: ${GITHUB_TARGET}\""
+echo "to add new source to git tree"
+echo "A submodule path have have been cached. To remove the submodule run:"
+echo "$ git rm --cached third_party/jitterentropy/jitterentropy-library/tests/raw-entropy/recording_userspace/jitterentropy"