I am trying to enable the pdo driver for my php installation, but when I runn the command
./configure --prefix=/usr/local/webserver/php --with-apxs2=/usr/loc
Try the packaged pecl version instead (the advantage of the packaged installs is that they're easier to upgrade):
apt-get install php5-dev
pecl install pdo
pecl install pdo_pgsql
or, if you just need a driver for PHP, but that it doesn't have to be the PDO one:
apt-get install php5-pgsql
Otherwise, that message most likely means you need to install a more recent libpq package. You can check which version you have by running:
dpkg -s libpq-dev