- Move the dependency of llvmjit-devel on clang and llvm to the
implementation packages where we can depend on the correct
versions.

- fix postgresql_has_llvm usage

- First round of changes to make it easier to build extensions for
- add postgresql-llvmjit-devel subpackage:
This package will pull in clang and llvm if the distro has a
recent enough version, otherwise it will just pull
postgresql-server-devel.
- add postgresql macros to the postgresql-server-devel package
those cover all the variables from pg_config and some macros
to remove repitition from the spec files