strace: set enableParallelBuilding = true
This reduces the build time from 55s to 25s on my modern 16-core machine.
The main motivation for this step is that I apply a custom patch onto
strace in my NixOS configuration and the build time is longer than necessary.
The debian package definition shows [0] that strace can be reliably build using
multiple makefile jobs.
[0] https://github.com/strace/strace/commit/0c56f62207d81713f9ce7705e865b75f921e6a1b
