Fix Docker postgres build

[rex993]

Docker postgres build failing, likely due to alpine15 update. Fixed by specify clang19 and llvm19

[jazzberry-ai]

Bug Report

Name: Potential incompatibility between pgvector and specific clang/llvm versions
Severity: Medium
Example test case: Building the Docker image with the patched Dockerfile. If the pgvector build fails, it indicates an incompatibility.
Description: The patch modifies the Dockerfile to use clang19 and llvm19 instead of the default clang and llvm. While this might be intended to provide more control over compiler versions, it introduces a risk of incompatibility with the pgvector build process. pgvector's build scripts might not be fully compatible with version 19 of clang/llvm, or it might have been previously tested and known to work with the default versions provided by the base image. Forcing a specific version could lead to build failures or unexpected behavior in pgvector.

_{Comments? Email us.}