CI: Test consuming the exported CMake configs.

.github/workflows/cmake_config.yml

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+name: cmake_config
+
+on: [push, pull_request]
+
+jobs:
+  cmake-check:
+    defaults:
+      run:
+        shell: bash
+    strategy:
+      matrix:
+        os: [windows-latest, macos-latest, ubuntu-latest]
+    runs-on: ${{ matrix.os }}
+    continue-on-error: false
+    name: ${{ matrix.os }}
+    steps:
+      - name: Setup Windows dependencies
+        if: runner.os == 'Windows'
+        uses: msys2/setup-msys2@v2
+        with:
+          update: true
+          install: >-
+            autoconf
+            automake
+            diffutils
+            libtool
+            gcc
+            git
+            patch
+            perl
+
+      - name: Setup macOS dependencies
+        if: runner.os == 'macOS'
+        run: brew install automake
+
+      - uses: actions/checkout@main
+
+      - name: Prepare source tree for build (Windows)
+        if: runner.os == 'Windows'
+        run: ./autogen.sh
+        shell: msys2 {0}
+
+      - name: Prepare source tree for build (Unix)
+        if: runner.os != 'Windows'
+        run: ./autogen.sh
+
+      - name: Configure
+        run: |
+          cmake -S . \
+                -B build \
+                -D CMAKE_BUILD_TYPE=Release \
+                -D CMAKE_INSTALL_PREFIX=$GITHUB_WORKSPACE/../local
+
+      - name: Build
+        run: cmake --build build --config Release --verbose
+
+      - name: Install
+        run: cmake --install build --config Release
+
+      - name: Consume from the build directory - Configure
+        run: |
+          cmake -S tests/cmake \
+                -B consumer-build \
+                -D CMAKE_BUILD_TYPE=Release \
+                -D LibreSSL_DIR=$GITHUB_WORKSPACE/build
+      - name: Consume from the build directory - Build
+        run: cmake --build consumer-build --config Release --verbose
+
+      - name: Consume from the install directory (CMAKE_PREFIX_PATH) - Configure
+        run: |
+          cmake -S tests/cmake \
+            -B consumer-install-prefix \
+            -D CMAKE_BUILD_TYPE=Release \
+            -D CMAKE_PREFIX_PATH=$GITHUB_WORKSPACE/../local
+      - name: Consume from the install directory (CMAKE_PREFIX_PATH) - Build
+        run: cmake --build consumer-install-prefix --config Release --verbose
+
+      - name: Consume from the install directory (LibreSSL_DIR) - Configure
+        run: |
+          cmake -S tests/cmake \
+                -B consumer-install-dir \
+                -D CMAKE_BUILD_TYPE=Release \
+                -D LibreSSL_DIR=$GITHUB_WORKSPACE/../local/lib/cmake/LibreSSL
+      - name: Consume from the install directory (LibreSSL_DIR) - Build
+        run: cmake --build consumer-install-dir --config Release --verbose

tests/cmake/CMakeLists.txt

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+cmake_minimum_required(VERSION 3.5)
+
+project(LibreSSL_Consumer LANGUAGES C)
+
+find_package(
+  LibreSSL
+  CONFIG
+  REQUIRED
+  COMPONENTS Crypto SSL TLS
+)
+
+set(RESULTS_TO_CHECK
+  "LIBRESSL_VERSION"
+  "LIBRESSL_FOUND"
+  "LIBRESSL_INCLUDE_DIR"
+  "LIBRESSL_LIBRARIES"
+  "LIBRESSL_CRYPTO_LIBRARY"
+  "LIBRESSL_SSL_LIBRARY"
+  "LIBRESSL_TLS_LIBRARY"
+)
+
+foreach(RESULT_VAR IN LISTS RESULTS_TO_CHECK)
+  if(${RESULT_VAR})
+    message(STATUS "${RESULT_VAR}: ${${RESULT_VAR}}")
+  else()
+    message(FATAL_ERROR "${RESULT_VAR} was not set by the package.")
+  endif()
+endforeach()
+
+add_executable(crypto crypto.c)
+target_link_libraries(crypto PRIVATE LibreSSL::Crypto)
+
+add_executable(ssl ssl.c)
+target_link_libraries(ssl PRIVATE LibreSSL::SSL)
+
+add_executable(tls tls.c)
+target_link_libraries(tls PRIVATE LibreSSL::TLS)

tests/cmake/crypto.c

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+#include <openssl/crypto.h>
+
+int main(void) {
+  OPENSSL_init_crypto(0, NULL);
+  OPENSSL_cleanup();
+  return 0;
+}

tests/cmake/ssl.c

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+#include <openssl/ssl.h>
+
+int main(void) {
+  SSL_library_init();
+  return 0;
+}

tests/cmake/tls.c

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+#include <tls.h>
+
+int main(void) {
+  tls_init();
+  return 0;
+}