Investigate how to accelerate the build time of FDB

Right now it's quite painfully slow to build FDB. This is an umbrella issue tracking efforts to make the build faster.

This is an old umbrella issue about slow FDB builds, but it names no build files, targets, benchmarks, or tests. Start by examining the repository's build process and measuring its main bottlenecks. Done would require a specific, validated build-time improvement and a focused follow-up change.

Written by the indexing model from the issue text.