This allows to use makefile rather than kaem script for building sed.
Makefiles for musl and mes are unified into one makefile with some
conditional code.
- Rename sources to distfiles for clarity.
- Per sys(a/c) distfiles to reduce rootfs.py processing and reduce RAM
usage in sysa.
- Canonicalise early kaem mes/tcc files to kaem script conventions.
- Cleanup unused setup in python.