Can't install mongo-php-driver on OS X 10.11
The problem was due to OS X 10.11 El Capitan's Rootless feature. To be able to install the extension into /usr/lib/php/* I had to temporarily disable the feature (instructions - please remember to re-enable it afterwards).
press cmd+r when booting up. Then go into utilities > terminal and type the following commands:
csrutil disablerebootdon't forget to enable it .