Extremely long build times

A year or two ago we noticed that build times were getting pretty slow. We did several things to improve this and brought down build times to around 4 1/2 minutes (on my setup). I don't know when or why this happened, but as of today, a full rebuild for me now takes ~9 minutes. Pretty much double the time it used to be.

This is esp. frustrating when you're working on the framework, which often requires a rebuild of most samples. Fixing a one-liner and having to wait up to 9 minutes to test something is pretty frustrating. That makes it almost impossible for me to actually work on that part of the samples.

We should take a look at why build times are so bad.

For comparison: A full rebuild of my own samples project (which includes ~100 projects) only takes about one minute.

Start by reproducing the full rebuild slowdown in the Vulkan samples project and compare it with the reported four-and-a-half-minute baseline and the one-minute own-samples build. Investigate the build path for the framework and samples to identify what caused the regression. Done means the source of the doubled build time is identified and build times are reduced or the remaining limitation is documented.

Written by the indexing model from the issue text.