lang/gcc5-aux: Minor bug fixes

When submitting patches to fix GNAT, I realized the exetime changes
were wrong. Moveover, the time patches not only are no longer needed,
but possibly bitrotted to the point of being wrong.

The next release of GCC5 (5.2) should have the FreeBSD unwind support
from gcc-trunk backported to GCC5 branch, so that should reduce the
patches by a lot. There are some minor changes involving NetBSD support
that are not used.

Also, apparently disable-libada functionality was broken by my patches,
but it's fixed now. This isn't used though.