So it looks like the new 'System Integrity Protection' lockdown of /usr (among other directories) makes pear and pecl a non-starter. Has anyone found a workaround short of disabling it?
There's a much easier way — no need to disable SIP or download your own copy:
sudo php /usr/lib/php/install-pear-nozlib.phar -d /usr/local/lib/php -b /usr/local/bin