Search for GNU-compatible dd for self-tests.

This checks for a dd that supports iflag=fullblock oflag=append,
and looks at gdd and dd for now, and warns of failing self-tests
if neither supports these two flags.

Signed-off-by: Matthias Andree <matthias.andree@gmx.de>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
8 files changed