Fixes source build of citus for alpine

[gurkanindibay]

For postgres 15.3 build failed. Added clang15 and llvm15-dev to fix the issue Reference: https://github.com/docker-library/postgres/commit/a3b0bb68faed03c6edd3978b8dd34ca67881f7c7#diff-263e4d92e2bddc6bbd3c9031218d17dfb38bd68d9e94f05d0604c41207944d98R47