Add libevent to GitHub integration CI (#1615)

### Issues:
Resolves CryptoAlg-2465

### Description of changes: 
Libevent already works with AWS-LC thanks to other compatibility work.
This adds a test to make sure it keeps working.

### Testing:
Tested the script locally but need to see what happens with GitHub
actions.

By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache 2.0 license and the ISC license.

---------

Co-authored-by: Justin W Smith <103147162+justsmth@users.noreply.github.com>

.github/workflows/integrations.yml

@@ -148,3 +148,16 @@ jobs:
       - name: Run strongswan build
         run: |
           ./tests/ci/integration/run_strongswan_integration.sh
+  libevent:
+    if: github.repository_owner == 'aws'
+    runs-on: ubuntu-latest
+    steps:
+      - name: Install OS Dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get -y --no-install-recommends install \
+          cmake gcc ninja-build golang
+      - uses: actions/checkout@v4
+      - name: Run libevent build
+        run: |
+          ./tests/ci/integration/run_libevent_integration.sh

tests/ci/integration/run_libevent_integration.sh

@@ -0,0 +1,38 @@
+#!/usr/bin/env bash
+# Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+# SPDX-License-Identifier: Apache-2.0 OR ISC
+
+set -exu
+
+source tests/ci/common_posix_setup.sh
+
+# Assumes script is executed from the root of aws-lc directory
+SCRATCH_FOLDER=${SRC_ROOT}/"scratch"
+AWS_LC_BUILD_FOLDER="${SCRATCH_FOLDER}/aws-lc-build"
+AWS_LC_INSTALL_FOLDER="${SCRATCH_FOLDER}/aws-lc-install"
+LIBEVENT_SRC="${SCRATCH_FOLDER}/libevent"
+export LD_LIBRARY_PATH="${AWS_LC_INSTALL_FOLDER}/lib"
+
+function build_and_test_libevent() {
+  pushd "${LIBEVENT_SRC}"
+  mkdir build && pushd build
+  cmake -GNinja -DOPENSSL_ROOT_DIR="${AWS_LC_INSTALL_FOLDER}" ../
+  ninja verify
+  popd && popd
+}
+
+# Make script execution idempotent.
+mkdir -p "${SCRATCH_FOLDER}"
+rm -rf "${SCRATCH_FOLDER:?}"/*
+pushd "${SCRATCH_FOLDER}"
+
+mkdir -p "${AWS_LC_BUILD_FOLDER}" "${AWS_LC_INSTALL_FOLDER}"
+git clone --depth 1 https://github.com/libevent/libevent.git
+
+# Test with shared AWS-LC libraries
+aws_lc_build "$SRC_ROOT" "$AWS_LC_BUILD_FOLDER" "$AWS_LC_INSTALL_FOLDER" -DBUILD_TESTING=OFF -DBUILD_TOOL=OFF -DCMAKE_BUILD_TYPE=RelWithDebInfo -DBUILD_SHARED_LIBS=1
+export LD_LIBRARY_PATH="${LD_LIBRARY_PATH:-}:${AWS_LC_INSTALL_FOLDER}/lib/"
+build_and_test_libevent
+
+ldd "${LIBEVENT_SRC}/build/lib/libevent_openssl.so" | grep "${AWS_LC_INSTALL_FOLDER}/lib/libcrypto.so" || exit 1
+popd