scripts: update distclean

The toolchains are now built in .build/ rather than in targets/
so distclean has to get rid of that.

We also clean up the old dir, as users may have old samples that
still refer to the old location.

Do not hide messages during distclean, and do not ignore errors.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

 This is NOT the official version of dialog.  This version has been

 significantly modified from the original.  It is for use by the Linux

 kernel configuration script.  Please do not bother Savio Lam with 

 questions about this program.