build: omit zlib pkg-config reference for Android

In both autotools and cmake builds, because Android does not offer
a `zlib.pc`.

Also:
- GHA/non-native: dump config files, to verify.

Reported-by: sfan5 on github
Fixes #21647

Closes #21648

.github/workflows/non-native.yml

@@ -297,6 +297,12 @@ jobs:
         if: ${{ !cancelled() }}
         run: cat bld/config.log bld/CMakeFiles/CMake*.yaml 2>/dev/null || true
 
+      - name: 'dump config files'
+        run: |
+          for f in libcurl.pc curl-config; do
+            echo "::group::${f}"; grep -v '^#' bld/"${f}" || true; echo '::endgroup::'
+          done
+
       - name: 'curl_config.h'
         run: |
           echo '::group::raw'; cat bld/lib/curl_config.h || true; echo '::endgroup::'