stdin_buf
use
The previous commit updated `rustfmt.toml` appropriately. This commit is the outcome of running `x fmt --all` with the new formatting options.
part of #121876
tools.mk
apparently I missed some tests in the last commit. Rather than having dozens of tests use the long version, use the short version in `run-make` and the long version in `run-make-fulldeps` (which is now only three tests)