SH Linux: remove big endian multilib

[NIIBE Yutaka]

The ABI of four targets are differents.  Hence, we need four libgcc-s.
Please understand this point.  We need four libgcc-s for sh-unknown-linux-gnu.

If we omit multilib support in sh-unknown-linux-gnu, say, we won't
have libgcc for -m4.  It still compiles program, yes, but doesn't link
(sometime it does with libgcc for -m3, but not always).

 > I've used that patch for a while now, but I'm in agreement with the others
 > that multilibs for Linux doesn't make much sense, when glibc doesn't
 > support it.

I agree with this more or less.  Using specified one is better and
simple.  But the definition of sh-unknown-linux-gnu is supporting four
targets.
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