I'm trying to install a PECL package on Linux, but the installer never gets past the configure stage.

My hosting provider mounted a file system at /var/tmp that prevents files from executing, and that's causing this error:

```
root@host [/usr/local/apache/conf/includes]# pecl install pdo
downloading PDO-1.0.3.tgz ...
Starting to download PDO-1.0.3.tgz (52,613 bytes)
.............done: 52,613 bytes
12 source files, building
running: phpize
Configuring for:
PHP Api Version:         20041225
Zend Module Api No:      20060613
Zend Extension Api No:   220060519
building in /var/tmp/pear-build-root/PDO-1.0.3
running: /root/tmp/pear/PDO/configure
checking for egrep... grep -E
checking for a sed that does not truncate output... /bin/sed
checking for cc... cc
checking for C compiler default output file name... a.out
checking whether the C compiler works... configure: error: cannot run C compiled programs.
If you meant to cross compile, use `--host'.
See `config.log' for more details.
ERROR: `/root/tmp/pear/PDO/configure' failed

```

I'm 99% sure the problem is that you can't execute files in /var/tmp (I copied an executable file over here and tried it to verify). I'm sure I can get PECL to complete if I have it do its build work somewhere else, but I can't find the appropriate configuration setting.

How do you tell PECL to build in a non-default folder?