1. Adds sha256sum stage to the bash build harness.
2. Adds a third argument to build(), the checksum file name. This is
used where there is more than one checksum file, most notably
in multi-stage compilations.
3. Adds checksum files to all remaining programs.
4. Adds appropriate 3rd argument where needed (coreutils, tcc-musl,
bison).
fosslinux