GHA: add workflow to compare configure vs cmake outputs

Uses scripts/cmp-config.pl two compare two curl_config.h files,
presumbly generated with configure and cmake. It displays the
differences and filters out a lot of known lines we ignore.

The script also shows the matches that were *not* used. Possibly
subjects for removal.

Closes #11964

.github/workflows/configure-vs-cmake.yml

@@ -0,0 +1,45 @@
+# Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
+#
+# SPDX-License-Identifier: curl
+
+name: configure-vs-cmake
+on:
+  push:
+    branches:
+    - master
+    paths:
+    - '*.ac'
+    - '**/*.m4'
+    - '**/CMakeLists.txt'
+    - 'lib/curl_config.h.cmake'
+    - 'scripts/cmp-config.pl'
+
+  pull_request:
+    branches:
+    - master
+    paths:
+    - '*.ac'
+    - '**/*.m4'
+    - '**/CMakeLists.txt'
+    - 'lib/curl_config.h.cmake'
+    - 'scripts/cmp-config.pl'
+
+permissions: {}
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v3
+
+    - name: run configure --with-openssl
+      run: |
+         autoreconf -fi
+         ./configure --with-openssl
+
+    - name: run cmake
+      run: |
+         mkdir build && cd build && cmake ..
+
+    - name: compare generated curl_config.h files
+      run: ./scripts/cmp-config.pl lib/curl_config.h build/lib/curl_config.h