Add the `g` flag to one of the regular expression substitutions in
`util/build-gnu.sh` so that all instances of `printf` are replaced
with `/usr/bin/printf` in `tests/dd/ascii.sh` instead of just one
instance per line.
* Fix regular expressions to only match when run the first time.
* Enhance the regular expression which removes duplicated "/usr/bin/" to
allow a space between them (+ also consider `init.cfg`).
Gnu checks before testing a utility whether that utility was actually built.
It thinks `arch` was not built, even though it was.
This patch does not convince gnu that `arch` was built (I wasn't able to figure that out),
but instead comments out the check in `init.cfg` when running `build-gnu.sh`.
When decoding an invalid base32/64 string, gnu writes everything it was
able to decode until it hit the decode error, while we don't write
anything if the input is invalid.
