GCC 6.1.0 native for OS X El Capitan, with GPL 2016 tools

Tools included:

Full GPL:

• ASIS, AUnit, and GDB from GNAT GPL 2016.
• Gprbuild from the public Git repository at commit c5c26c2683fcdd9c1fc684274faaad1b30c762e1

GPL with Runtime Library Exception:

• GNATCOLL from the public GIT repository at commit 719fae1d0b60c31a9f7c0de8b0a143fa57449b47
• XMLAda from the public Git repository at commit 8a9536bf161125cb1e12da376e8d7b51f1b33677