PHP PECL and /tmp
When you are forced to install a php module via pear/pecl, it will probably winge about autoconf despite it being installed. The error is confusing, the actual problem is that it creates a script in /tmp and attempts to execute it, even though /tmp is mounted noexec.
The solution is to temporarily remount /tmp as executable:
$ mount -o remount,exec /tmp $ pecl install oauth $ mount -o remount,noexec /tmp