An export in a shell script does not leak out:

```
derick@whisky:~/dev/php/derickr-mongo-php-driver $ echo $CFLAGS

[GIT: fix-tests-2.5][PHP: 5.5.8-dev  ]
derick@whisky:~/dev/php/derickr-mongo-php-driver $ ./rebuild.sh 2>&1 >/tmp/log
[GIT: fix-tests-2.5][PHP: 5.5.8-dev  ]
derick@whisky:~/dev/php/derickr-mongo-php-driver $ echo $CFLAGS

[GIT: fix-tests-2.5][PHP: 5.5.8-dev  ]
```