Import lang/gcc5-aux based on gcc-5.1

This compiler package is not like the lang/gcc4* packages, but rather
the lang/gcc-aux package which exists to bring GNAT, the Ada language
compiler.  The lang/gcc-aux package is based on gcc-4.9, and this
package is based on gcc-5.  This is the first gcc5 package in pkgsrc,
and it does support C, C++, ObjC, and Fortran in addition to Ada thus
it is very useful, but it does have a different purpose than other
gcc ports.

This port has had minimal testing.  I verified GNAT passes 100% of the
testsuite on NetBSD 6.1/amd64, but it has not been tested on any
NetBSD 5, 7.0 or 7.99 platform yet.  I don't have any hardware, so it
will require using a VM or having others report failure/success.  Due
to similarity with lang/gcc-aux, chances are good that it will build
and function properly on other platforms.

See http://gcc.gnu.org/gcc-5/changes.html for more information about
improvements over the gcc-4.9 series.

(marino)