gnunnet: halt build if any command fails

gnunnet: halt build if any command fails

There are many places in the packages' install recipes whith multiple
commands being executed in the same shell invocation, separated with a
semicolon (;).  The return status will depend only on the last command
being run.  The same thing happens in loops, where only the last file
will determine the result of the command.

Change the ';' to '&&', and exit the loop if any operation fails.

Signed-off-by: Eneas U de Queiroz <cotequeiroz@gmail.com>