GCC 4.9 vs. GCC 5.3 vs. GCC 6.1 On A Debian Xeon E5 Linux System

Given the recent stable release of GCC 6 (GCC v6.1.0), here are some fresh compiler benchmarks on an Intel Debian x86_64 system when comparing the GCC 4.9.3, GCC 5.3.0, and GCC 6.1.0 compiler releases.