Log Message:
Upgrade USE_LANGUAGES=ada to use lang/gcc5-aux instead of lang/gcc-aux

This large commit accomplishes the following:

1) Switch USE_LANGUAGES=ada to require lang/gcc5-aux (gcc 5.4) instead
   of lang/gcc-aux (gcc 4.9.2) on gcc.mk
2) Bump affected ports and fix paths as necessary
3) Upgrade devel/gprbuild to the latest release
   - No longer requires lang/gnat_util
   - gprslave requires gcc6-aux, so it was disabled for now
4) Fix lang/gnat_util but set PKG_SKIP_REASON
   - It has no further purpose in the pkgsrc tree
   - It has no practical purpose outside of the pkgsrc tree
   - Indicate intent to remove from tree in Jan. 2017
5) Set devel/GPS as failed with PKG_FAIL_REASON
   - This version of GPS is several years old and at the time they were
     strongly tied to compiler.
   - Latest release of GPS require gcc6-aux (not available) and several
     new and complex dependencies
   - maintainer (me) has no interest to continue supporting it
   - Leaving GPS in place until Jan 2017 to give another person chance to
     upgrade and take over support
   - Latest version in FreeBSD Ports Collection as a reference point