krb5: Make compile_et.sh quiet during builds

[markj]

Summary

This script is run during buildworld and prints a bunch of debug output.
It's intrusive and probably not needed, at least by default, so let's
make the build output a bit cleaner. This is an upstream script, but it
hasn't been modified in 15 years so the local modification is unlikely
to cause any pain.

[markj]

Silence another message which otherwise appears during make -s output.