This tip was really good! I did the test here on Windows 10, with gcc 12.2.0, Built by MinGW-W64 project.
`koch boot -d:release` on the first build took 00:01:38.10 (98.10s total). On the second build it only took 00:00:28.67 (28.67s total). The initial nim.exe is from csources_v2 for both and I'm building the devel version. Note: I deleted nimcache before.
