croutonwheel: Replace awk by mawk

-W interactive is not POSIX, and does not exist in gawk.

croutonwheel would break if the user installs gawk, for example (it replaces /usr/bin/awk).

A POSIX way of doing this would be to use "fflush()" after each print, but that does not seem to work with mawk (it still needs the -W interactive parameters)...