Waiting for autoconf to finish is annoying. But have you ever considered how much time and effort is wasted every day doing that? Neither have I, but let's estimate it anyway.
First we need an estimate of how many projects are using Autotools. 100 is too low and 10 000 is probably too high, so let's say 1000. We also need an assumption of how long an average autoconf run takes. Variability here is massive ranging from 30 seconds to (tens of) minutes on big projects on small hardware. Let's say an average of one minute as a round number.
Next we need to know how many times builds are run during a day. Some projects are very active with dozens of developers whereas most have only one person doing occasional development. Let's say each project has on average 2 developers and each one does an average of 4 builds per day.
This gives us an estimate of how much time is spent globally just waiting for autoconf to finish:
1000 proj * 2 dev/proj * 2 build/dev * 1 minute/build =
4000 minutes = 66 hours
66 hours. Every day. If you are a business person, feel free to do the math on how much that costs.
But it gets worse. Many organisations and companies build a lot of projects each day. As an example there are hundreds of companies that have their own (embedded) Linux distribution that they do a daily build on. Linux distros do rebuilds constantly and so on. If we assume 10 000 organisations that do a daily build and we do a lowball estimate of 5 dependencies per project (many projects are not full distros, but instead build a custom runtime package or something similar), we get different numbers:
10 000 organisations * 1 build/organisation * 5 dependencies/build * 1 min/dependency = 50 000 minutes = 833 CPU hours
That is, every single day over 800 CPU hours are burned just to run autoconf. Estimating CPU consumption is difficult but based on statistics and division we can estimate an average consumption of 20 Watts. This amounts to 16 kWh every day or, assuming 300 working days a year, 5 MWh a year.
That is a lot of energy to waste just to be absolutely sure that your C compiler ships with stdlib.h.