Title: #291: BUILD: Improve error messages for optional dependencies
sssd-kcm is enabled by default and build failed in case of `configure --without-secrets`
due to missing dependency on libjansson. It should fail at configure time.
Patch also improve hints for missing optional dependencies
To pull the PR as Git branch:
git remote add ghsssd https://github.com/SSSD/sssd
git fetch ghsssd pull/291/head:pr291
git checkout pr291