Plugin update hangs after "Updating Plugin X"

I have a multisite installation. I recently upgraded our Apache/PHP/cURL stack. I suspect this problem is in some cURL-PHP configuration that I did wrong.

Apache 2.2.31 (apr 1.5.2 apr-util 1.5.4 pcre 8.37)
curl 7.45.0
php 5.6.15

* I tried Chrome and Firefox. The browser seems irrelevant.

* SCRIPT_DEBUG had no effect

* The behavior is the same whether updating one plugin or all the plugins. I did try network deactivating all the plugins, and that made no difference. But, I didn’t go around to the individual sites to be sure they weren’t active locally.

* By printing messages to a file, I found that the code gets stuck in wp-admin/includes/class-wp-upgrader.php at line 980

* I’m having a devil of a time finding an error message. PHP is sending messages to the apache error_log, but the messages all seem unrelated and occur whether or not an update is being attempted.

The code where the hang happens is:

$result = $this->run( array(
‘package’ => $r->package,
‘destination’ => WP_PLUGIN_DIR,
‘clear_destination’ => true,
‘clear_working’ => true,
‘is_multi’ => true,
‘hook_extra’ => array(
‘plugin’ => $plugin
)
) );

This corresponds to this entry in access_log:

GET /PATH_CURRENT_SITE/wp-admin/network/update.php?action=update-selected&plugins=PLUGIN%2FPLUGUIN.php&_wpnonce=b95778e572

I built curl like so:

./configure –prefix=/path/to/curl-7.45.0

I built php like:

./configure –prefix=/path/to/php-5.6.15 –enable-bcmath –with-zlib=shared –with-bz2 –with-curl=/path/to/curl-7.45.0 –enable-ftp –with-apxs2=/path/to/httpd-2.2.31/bin/apxs –with-mysql