Special Points in This build script: https://github.com/jackywei/HOW-TO-BUILD-HHVM-WiKi/wiki/_pages
1. Support non-internet environment build
2. Total 5 scripts for build whole hhvm, including upgrade gcc.


To Build HHVM in CentOS5.2, please refer to CentOS5.2_HHVM
To Build HHVM in CentOS6.3, Please refer to CentOS6.3_HHVM
To learn How to use HHVM, please refer to HHVM_Usage(ongoing)