Fix build errors with HHVM 3.7
Fix build errors with HHVM 3.7

craig-russell/hhvm-newrelic-ext,chregu/hhvm-newrelic-ext,chregu/hhvm-newrelic-ext,KMK-ONLINE/hhvm-newrelic-ext,KMK-ONLINE/hhvm-newrelic-ext,deivisonarthur/hhvm-newrelic-ext,Qoto/hhvm-newrelic-ext,craig-russell/hhvm-newrelic-ext,effeks/hhvm-newrelic-ext,deivisonarthur/hhvm-newrelic-ext,craig-russell/hhvm-newrelic-ext,effeks/hhvm-newrelic-ext,deivisonarthur/hhvm-newrelic-ext,Qoto/hhvm-newrelic-ext,chregu/hhvm-newrelic-ext,effeks/hhvm-newrelic-ext,KMK-ONLINE/hhvm-newrelic-ext,Qoto/hhvm-newrelic-ext