Support for alpha-osf, mips-irix

[Rainer Orth]

Every once in a while I come across references to Tru64 UNIX
(alpha*-dec-osf*) and SGI IRIX in the binutils-gdb tree.  This seems
strange given that the last versions supported by GCC (Tru64 UNIX V5.1
and IRIX 6.5) were obsoleted in GCC 4.7 back in 2012 and removed in GCC
4.8.  GDB took a bit longer, but GDB 7.9 removed support for both as
well in 2015, although a few references have been overlooked.

Both platforms are long obsolete and I strongly suspect there's no one
to benefit from continued support (whatever that means) in binutils alone.

Any objections to removing support completely?  I'm not yet certain how
either or both is entangled with code for other targets still supported
(alpha-linux, mips-linux).

There's even more prehistoric cruft, btw., e.g. references to
mips-ultrix ;-)

	Rainer

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Rainer Orth, Center for Biotechnology, Bielefeld University