Build process: mpy file in frozen dir produces spam
I inadvertently included a .mpy file in a directory containing .py files for freezing. On building, so much output spewed that the Bash history buffer filled; I couldn't scroll back far enough to see where the error first occurred.
It would be good if the build process either stopped with a clear message or ignored files without .py extensions with a warning.
mpy-cross: Do not automatically build mpy-cross, rather do it manually.
Building mpy-cross automatically leads to some issues with the build process and slows it down (see eg #3255, #3987, #4733). Instead, require it to be built manually.
mpy-cross is pretty stable now, and well known by users, so I think it's only a minor inconvenience to require it to be built manually (roughly once each release), and this is a simple way to fix a lot of problems with having it auto-built.