When you tried to install something and you got 'phpize failed' type of error, check the following:
php -i | grep 'enable-sigchild'
If your installation of PHP was compiled with the –enable-sigchild flag on, then the return value from a pclose() call can’t be trusted. One of PEAR’s components, called PEAR::Builder, uses pclose() as part of the package installation process, to try to determine whether a given operation succeeded or not.
Even though the operation succeeds, pclose() returns -1, signaling a failure, and the rest of PEAR then takes pclose() at its word.
The solution (beside recompiling php without the flag) is posted here. It consists in a patch applied to /usr/lib/php/PEAR/Builder.php. Easy and great fix!
Tested with success on different Slackware flavors (but must be working on the rest too).