This update for postgresql13 fixes the following issues:

- Upgrade to 13.6: (bsc#1195680)
  * https://www.postgresql.org/docs/13/release-13-6.html
  * Reindexing might be needed after applying this upgrade, so
  please read the release notes carefully.
- Add constraints file with 12GB of memory for s390x as a workaround. (bsc#1190740)
- Add a llvmjit-devel subpackage to pull in the right versions
  of clang and llvm for building extensions. 
- Fix some mistakes in the interdependencies between the
  implementation packages and their noarch counterpart.
- Update the BuildIgnore section.